Central London has seen the longest stretch of high temperatures in almost six decades, as more thunderstorms are forecast across the UK.
The Met Office has said temperatures surpassed 34C in the capital for the sixth day in a row - the first time that has happened since at least 1961.
A yellow storm warning is in place for the whole of England, Wales and parts of Scotland on Wednesday.
Those regions could see flooding, travel disruption and power cuts.
The Met Office also warned of potential damage to buildings from lightning strikes or strong winds, and 30 to 40mm of rain falling in less than an hour in some places.
The yellow warning is in place for much of England and Wales until Monday night next week.
The force said it saw an increase in anti-social behaviour and public order offences on Saturday and Sunday.
Assistant Chief Constable Jim Colwell said the weekend's events, spurred on by the hot weather, had forced officers to attend a "plethora of different incidents".
Steve Andrews, head of central operations for South East Water, said more than 150 million litres of extra water were being pumped into the network as the UK heatwave continues.
France and the UK have been once again dragged into debating each other's role in containing and managing the flow of migrant boats across the Channel. Britain has demanded Paris invest more to ensure the presence of sufficient Border Patrol officials to return vessels trying to enter the UK to their departure points across the French coast. But speaking to France 3 Hauts-de-France, the Mayor of Calais Natacha Bouchart warned Boris Johnson the UK's conduct in recent days is tantamount to having declared "maritime war" on France.
Ms Bouchart said: "It is a declaration of maritime war.
"The British are creating this themselves by not wanting to review their reception arrangements, by contenting themselves with giving lessons and by subjecting Calaisians to this situation for too long."
The Calais mayor also insisted the UK should focus its attention in reviewing its migration policies as she warned the citizens of Calais remain opposed to forced returns to France from Britain.
She continued: "It's like arm-wrestling, it's what they're used to doing.
"Technically, I don't even see how they can achieve this. And I think the Government will be opposed. In any case, we are are opposed here.
"But rather than accepting migrants who work illegally - this is in fact their future in England - rather than giving lessons, it would be better than tabling legal texts to review reception conditions in their country."
Home Secretary Priti Patel at the weekend suggested she would ask the Department of Defence to deploy the Royal Navy in the Channel to monitor the British coast and prevent the docking of migrant vessels.
The Home Secretary insisted she wanted to make the English Channel path "unviable" as she insisted the UK was committed to putting an end to the criminal network facilitating the arrival of new boats.
“We are going to be working at pace in the coming days to make that plan a reality.”
The UK is bound by the EU Dublin III Regulation which set out the responsibilities of member states in regards to asylum seeking until the end of the Brexit transition period.
Former French Ambassador Gérard Araud pointed out London will need to renegotiate its current migratory checks arrangements with Paris after the Dublin III regulations lapses in December 2020.
Mr Araud responded to Ms Patel's demands for additional French help on Twitter: "Actually, Madam Secretary, as you may know, the cooperation with France was enshrined in the EU rules.
"You’ll have to negotiate a new treaty with your neighbor."
Prime Minister Boris Johnson said: "I am saddened to learn of the very serious incident in Aberdeenshire and my thoughts are with all of those affected. My thanks to the emergency services at the scene."
The chief executive of Network Rail, Andrew Haines, is cutting short his family holiday in Italy.
He will fly back to the UK on Wednesday afternoon and then head to the site.
The incident took place at Carmont near Stonehaven as torrential rain and thunderstorms caused flooding and travel disruption across many parts of central and eastern Scotland.
Ms Sturgeon said the derailment had happened in "a very difficult location for emergency services to access".
She added: "I know and appreciate that there will be many families who will be anxious if they believe they had relatives who were on that train.
"We will do everything we can to make sure the emergency services are supported, that families are supported."
The train was made up of two locomotives - at the front and back - and four carriages.
It is understood that the front locomotive and three passenger carriages have left the track and are now sitting on an embankment.
British Transport Police said its officers had been called to the scene of the derailment at about 09:43.
A few minutes later, Network Rail tweeted that there had been reports of a landslip at Carmont.
NHS Grampian confirmed it was on a "major incident footing", and ScotRail said it was assisting the emergency services.
Kevin Lindsay, the Scottish organiser for train drivers' union Aslef, said: "We are aware that this is an extremely serious incident and our thoughts are with everyone involved."
The RMT union's Mick Lynch said: "The facts behind this incident will need to be established in due course, but at this stage we are focussed on support and assistance and our thoughts are with all those impacted by this tragedy."
Are you in the area? Did you witness the incident? If it is safe to do so please share your experiences by emailing haveyoursay@bbc.co.uk.
Please include a contact number if you are willing to speak to a BBC journalist.
Prime Minister Boris Johnson said: "I am saddened to learn of the very serious incident in Aberdeenshire and my thoughts are with all of those affected. My thanks to the emergency services at the scene."
The incident took place at Carmont near Stonehaven as torrential rain and thunderstorms caused flooding and travel disruption across many parts of central and eastern Scotland.
The train was made up of a locomotive and four carriages.
It is understood the locomotive and three carriages derailed and slid down an embankment.
Network Rail had reported a landslip at Carmont.
British Transport Police said its officers had been called to the scene of the derailment at about 09:43.
NHS Grampian confirmed it was on a "major incident footing", and ScotRail said it was assisting the emergency services.
Kevin Lindsay, the Scottish organiser for train drivers' union Aslef, said: "We are aware that this is an extremely serious incident and our thoughts are with everyone involved."
The RMT union's Mick Lynch said: "The facts behind this incident will need to be established in due course, but at this stage we are focussed on support and assistance and our thoughts are with all those impacted by this tragedy."
Are you in the area? Did you witness the incident? If it is safe to do so please share your experiences by emailing haveyoursay@bbc.co.uk.
Please include a contact number if you are willing to speak to a BBC journalist.
