Rishi Sunak's judgement is under scrutiny after cabinet minister Sir Gavin Williamson quit vowing to clear his name over bullying claims.
Mr Sunak faces Prime Minister's Questions where he is set to be grilled on what he knew about the allegations.
Sir Gavin is accused of abusive behaviour towards MPs and civil servants but denies any wrongdoing.
Labour said the PM, who promised a government of integrity, had shown "poor judgement" in appointing him.
Sir Gavin was appointed minister without portfolio after Mr Sunak, a political ally, won the Tory leadership and became prime minister just two weeks ago.
The BBC understands the pair met on Tuesday evening for their first detailed discussion about the allegations, after which Sir Gavin made the decision to resign.
In his resignation letter, the MP said claims about his conduct had become a "distraction" but defiantly vowed to "clear my name of any wrongdoing".
In reply, Mr Sunak said he accepted the resignation "with great sadness" and thanked Sir Gavin for his "personal support and loyalty".
Complaints against Sir Gavin first emerged when The Sunday Times published a series of expletive-laden texts he sent last month to then-chief whip Wendy Morton.
In the texts, he appears to complain about not having been invited to the Queen's funeral, and seemingly accuses Ms Morton of "rigging" ticket allocations against MPs not "favoured" by then-prime minister Liz Truss.
He reportedly warned Ms Morton "not to push him about" and said that "there is a price for everything".
A senior civil servant later told the Guardian that, during his time as defence secretary, Sir Gavin told them to "slit your throat" and, on another occasion, to "jump out of the window".
On Tuesday, his former deputy, Anne Milton, also claimed he had behaved in a "threatening" and "intimidating" way towards MPs while serving as chief whip.
Ex-Conservative Party Chair Jake Berry has said he told Mr Sunak about Ms Morton's complaint on 24 October, the day before Sir Gavin's appointment.
No 10 has said the prime minister "knew there was a disagreement" but that he didn't know the "substance" of the messages until they were published by the Sunday Times.
October 25: Mr Sunak becomes PM and appoints Sir Gavin to the cabinet as a minister without portfolio
November 5: Expletive-laden text messages sent by Sir Gavin to Ms Morton are published by the Sunday Times
November 6: Mr Sunak says the messages are "not acceptable" and acknowledges he is aware of a disagreement between Sir Gavin and Ms Morton
November 7: The PM says he will wait for the results of a complaints investigation into Sir Gavin "before making any decisions about the future"
Later, a Guardian story claims Sir Gavin told a senior civil servant to "slit your throat", when he was defence secretary, something he denies
November 8: Sir Gavin's texts to Ms Morton are referred to the ICGS, the parliamentary watchdog
Shortly after 20:00, Sir Gavin resigns claiming the allegations against him were becoming a distraction
There are still questions being asked about why Gavin Williamson was appointed in the first place.
Some Conservative MPs are angry he was brought back into cabinet; both because of his reputation but also because he was sacked in the past over the leak of a document relating to national security.
Opposition parties argue the appointment showed the prime minister was weak and had to compromise the integrity he promised to try and unite his party with a diverse cabinet.
Number 10 disagrees. They say the details of allegations against Sir Gavin only became clear in recent days.
In comparison with some of the recent turmoil at Westminster, things have seemed a bit calmer since Rishi Sunak took over.
But there have been real tensions over Sir Gavin's appointment and that of Suella Braverman. Some of those tensions have hints of factionalism; centrists who didn't like Ms Braverman or Liz Truss allies who disliked Sir Gavin.
There are still unhappy Conservative MPs who have the ability to make life difficult for Number 10. Unity is normally easier talked about that achieved.
Sir Gavin has been reported to the MPs' bullying watchdog, the Independent Complaints and Grievance Scheme, over his WhatsApp messages to Ms Morton.
The Guardian has reported that the civil servant from the Ministry of Defence has also lodged a complaint with the body.
Sir Gavin's resignation marks the third time he has been forced from government. In 2019, he was sacked as defence secretary after allegedly leaking sensitive information related to Huawei's potential involvement in the UK's 5G network.
Later that year, he was made education secretary by Boris Johnson, but in 2021 was removed over his handling of A-level exams during the Covid-19 pandemic.
Deputy Labour leader Angela Rayner called Sir Gavin's appointment last month "astonishing" and said it showed "poor judgement and lack of leadership and weakness" on the part of the prime minister.
She said Sir Gavin should stand down as an MP if the bullying claims are proven.
Liberal Democrat deputy leader Daisy Cooper questioned why Mr Sunak had stood by Sir Gavin, saying his "promise to lead a government of integrity has now been left in tatters".
But defending Mr Sunak's judgement, Education Secretary Gillian Keegan said the prime minister was not aware of any specific allegations made against Sir Gavin.
She added that it was "always sad to lose a colleague, particularly in these kind of circumstances - these are people with families".
In his resignation letter, Sir Gavin said he refuted the "characterisation" of the claims "about my past conduct" but felt they had become a "distraction from the good work the government is doing".
He added that he had apologised to the recipient of the text messages and would comply with the complaints process.
He later tweeted that he would not be taking any severance pay, traditionally given to ministers when they leave office.
"Your commitment to successive Conservative governments and the party over the years has been unwavering," Mr Sunak said in reply.
Mr Sunak is also facing pressure over why he reappointed Suella Braverman as home secretary just weeks after she was forced to resign for breaking ministerial rules by sending an official document to a fellow MP from her personal email.
Opposition figures have again accused him of keeping her in the cabinet as part of an agreement to ensure her support for his position as prime minister.
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Many nurses needing to use food banks are doing so because of a broken "relationship or boiler", Education Secretary Gillian Keegan has suggested.
Ms Keegan told Sky News that "of course" she clapped for nurses during the pandemic.
But asked whether she is comfortable with nurses now being forced to use food banks, she replied: "Quite often when you go to food banks, something will have happened, you know, something will have broken down - either a relationship or boiler or anything.
"Usually they're in an emergency situation."
Sunak to face grilling over Williamson appointment - Politics latest
Ms Keegan also told nurses there is no point in going on strike over pay.
"I don't think there's any point in going on strike," she told Kay Burley.
"I would urge the nurses to continue those discussions, but the reality is if we gave massive above-inflation rises, not only would we have to raise a lot more money, but it would actually fuel inflation.
"This is the problem. We really have to tackle inflation."
It comes as a nursing union representing hundreds of thousands of nurses in the UK is expected to vote to hold the first nationwide strike in its 106-year history.
The Royal College of Nursing (RCN) had urged more than 300,000 of its members to vote for industrial action over pay in the union's biggest strike ballot.
The result of the ballot will be announced later today.
The RCN has called for its members to receive a pay rise of 5% above the RPI inflation rate, which currently stands at above 12%.
This request has not been met by any UK nation.
Although the details of the potential strike action are yet to be determined, patients are likely to face disruption to operations and appointments.
Oliver Dowden, the chancellor of the duchy of Lancaster, previously told Sky News' Sophy Ridge on Sunday programme that the government has "well-oiled" contingency plans in place for dealing with any strike by nurses.
In the event of industrial action, the NHS would prioritise the most essential services, he said.
Read more:
More than 15,000 ambulance workers to vote on strike
Higher pay offer for nurses unlikely to be put on the table
Recent analysis showed an experienced nurse's salary has fallen by 20% in real terms since 2010, the RCN said, adding that nurses are working the equivalent of one day a week for nothing.
Health workers in other unions, including ambulance staff, hospital porters and cleaners, are also voting on industrial action over pay.
A Department of Health and Social Care spokesperson said: "We value the hard work of NHS staff including nurses, and are working hard to support them - including by giving over one million NHS workers a pay rise of at least £1,400 this year as recommended by the independent NHS Pay Review Body, on top of 3% last year when pay was frozen in the wider public sector.
"Industrial action is a matter for unions, and we urge them to carefully consider the potential impacts on patients."
Just Stop Oil has told ITV Meridian its protesters have returned to the M25 motorway this morning.
The campaign group said it has targeted 5 locations on Britain's busiest motorway, bringing traffic to a standstill.
It also told ITV Meridian it is working with fellow group, Animal Rebellion, in this morning's protests.
This morning has seen wide-scale disruption to journey's and several incidents on the M25.
On the northern part of the M25 Essex Police said it has arrested a person for 'causing a public nuisance' on the motorway whilst dealing with an incident.
One of their officers were struck while implementing a rolling road block to protect the pedestrian in the road between J26 and J27.
On the same stretch a lorry was involved in a collision, causing further delays for commuters.
Police have since closed the road clockwise.
Traffic monitoring service, Inrix, is reporting the road has been closed clockwise between Junction 7 for Gatwick Airport and 8 for Reigate due to the protesters.
Traffic has backed up to Gatwick Airport on the M23 as drivers try to use extremely busy local a-roads.
Meanwhile, in the anticlockwise direction the road has been closed between 9 for Leatherhead and 8 for Reigate.
National Highways is also reporting protesters have targeted the road between Junction 4 and Junction 5 for the M26.
Currently two lanes are closed in a clockwise direction between the two junctions, causing traffic to build up.
Protests have now been reported on the M25 near to Heathrow Airport, with the anticlockwise blocked, delays due to demonstration between J14 A3113 Airport Way (Heathrow) and J13 A30 (Staines).
Elsewhere, all traffic is being temporarily held and queueing for two miles due to further protests on the M25 clockwise before J30 for A13
Essex Police has sent a specialist officer, trained to work at heights to remove the individual from the gantry at Junction 30.
A similar operation is now in force at Junction 29, where another person has climbed a gantry there.
Yesterday much of the M25 was brought to a standstill due to protests by Just Stop Oil, who had targeted multiple sections of the motorway.
Efforts to disperse Tuesday's protests across the road involved the Metropolitan, Surrey, Kent and Essex police forces.
They have asked people stuck in traffic as a result of protesters to stay in their vehicles and not obstruct the hard shoulder.
This is a developing story. More to follow.
The Royal College of Nursing is expected to announce today that nurses have voted to take strike action in many parts of the country.
Some hospitals, not all, will take action, it is believed.
The strike ballot among more than 300,000 members of the RCN was the biggest in the union's 106-year history and marks the first national action over a pay dispute.
An RCN spokesperson told Sky News: "Our strike action will be as much for patients as it is for nurses - we have their support in doing this.
"As we begin action, politicians in every part of the UK will be challenged to back their nursing staff and understand the strength of public support."
Although the details of the strike action are yet to be determined, patients are likely to face disruption to operations and appointments.
The union is campaigning for a pay rise of 5% above inflation.
Oliver Dowden, the chancellor of the duchy of Lancaster, previously told Sky News that the government has "well-oiled" contingency plans in place for dealing with any strike by nurses.
In the event of industrial action, the NHS would prioritise the most essential services, he said.
Recent analysis showed an experienced nurse's salary has fallen by 20% in real terms since 2010, the union said, adding that nurses are working the equivalent of one day a week for nothing.
The RCN said there are record nursing vacancies and in the past year 25,000 nursing staff around the UK left the Nursing and Midwifery Council register.
Read more:
More than 15,000 ambulance workers to vote on strike
Higher pay offer for nurses unlikely to be put on the table
The NHS could also be in line for a further tightening of budgets as Jeremy Hunt, the chancellor, faces the challenge of tackling a £50bn hole in public finances.
Last month Therese Coffey, the health secretary at the time, said the government is "not anticipating" having to put a higher pay offer for nurses on the table as they voted on strike action.
Prime Minister Rishi Sunak is facing questions about his judgement following the resignation of cabinet minister Sir Gavin Williamson after bullying claims.
Mr Sunak is set to face MPs at Prime Minister's Questions and is expected to be asked when he learned the full details of the allegations.
Sir Gavin is accused of abusive behaviour towards fellow MPs and civil servants, though denies any wrongdoing.
Labour said the episode has shown "poor judgement and leadership" by Mr Sunak.
Sir Gavin was appointed minister without portfolio after Mr Sunak, a close political ally, won the Tory leadership just two weeks ago.
Complaints against him first emerged when The Sunday Times published a series of expletive-laden texts he sent last month to then-chief whip Wendy Morton.
In the texts, he appears to complain about not having been invited to the Queen's funeral, and seemingly accuses Ms Morton of "rigging" ticket allocations against MPs not "favoured" by then-prime minister Liz Truss.
He reportedly warned Ms Morton "not to push him about" and said that "there is a price for everything".
A senior civil servant later told the Guardian that, during his time as defence secretary, Sir Gavin told them to "slit your throat" and, on another occasion, to "jump out of the window".
On Tuesday, his former deputy, Anne Milton, also claimed he had behaved in a "threatening" and "intimidating" way towards MPs while serving as chief whip.
Ex-Conservative Party Chair Jake Berry has said he told Mr Sunak about Ms Morton's complaint on 24 October, the day before Sir Gavin's appointment.
No 10 has said the prime minister "knew there was a disagreement" but that he didn't know the "substance" of the messages until they were published by the Sunday Times.
Sir Gavin has been reported to the MPs' bullying watchdog, the Independent Complaints and Grievance Scheme, over his WhatsApp messages to Ms Morton.
The Guardian has reported that the civil servant from the ministry of defence has also lodged a complaint with the body.
Speaking on Monday, Mr Sunak said the language used in the texts was "not acceptable", but asked if it amounted to bullying said it was "right" to let an independent complaints process conclude.
Sir Gavin's resignation marks the third time he has been forced from government. In 2019, he was sacked as defence secretary after allegedly leaking sensitive information related to Huawei's potential involvement in the UK's 5G network.
Later that year, he was made education secretary by Boris Johnson, but in 2021 was removed over his handling of A-level exams during the Covid pandemic.
Speaking on BBC Two's Newsnight, deputy Labour leader Angela Rayner called Sir Gavin's appointment last month "astonishing" and said it showed "poor judgement and lack of leadership and weakness" on the part of the prime minister.
She said Sir Gavin should stand down as an MP if the bullying claims are proven. "There is no place for bullies in parliament," she said.
David Lammy, shadow foreign secretary, told BBC Radio 4's Today Programme that Sir Gavin's behaviour was "repellent, odious and unacceptable" and questioned why he had been appointed to a ministerial position in Mr Sunak's government.
"He appointed him as some sort of enforcer - apparently because this is the way he behaves," Mr Lammy said.
"We really should have an account of why he came back into government - it's not clear in the first place why this individual was knighted for services to this country."
Liberal Democrat deputy leader Daisy Cooper said: "Rishi Sunak has serious questions to answer about why he appointed Gavin Williamson, then stood by him instead of sacking him.
"His promise to lead a government of integrity has now been left in tatters."
In his resignation letter, Sir Gavin said he refuted the "characterisation" of the claims "about my past conduct" but felt they had become a "distraction from the good work the government is doing".
He added that he had apologised to the recipient of the text messages and would comply with the complaints process to "clear my name of any wrongdoing".
He later tweeted that he would not be taking any severance pay, traditionally given to ministers when they leave office.
In reply, Mr Sunak said he accepted the resignation "with great sadness" and thanked Sir Gavin for his "personal support and loyalty".
"Your commitment to successive Conservative governments and the party over the years has been unwavering," he said.
Mr Sunak is also facing pressure over why he reappointed Suella Braverman as home secretary just weeks after she was forced to resign for breaking ministerial rules by sending an official document to a fellow MP from her personal email.
Opposition figures have again accused him of keeping her in the cabinet as part of an agreement to ensure her support for his position as prime minister.
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