Pictures from Brighton beach today

The mercury rose to a scorching 33.3C (91.94F) at Heathrow Airport in west London on Thursday, beating Wednesday's high of 32.6C (90.68F) at the same location.

Scotland also had its highest temperature so far this year with the thermometer reaching 30C (86F) in Prestwick.

Chief medical officer for England Professor Chris Whitty urged people to follow social distancing rules in the hot weather or risk causing a spike in coronavirus.

He wrote on Twitter: "Covid-19 has gone down due to the efforts of everyone but is still in general circulation.

"If we do not follow social distancing guidance then cases will rise again.

"Naturally people will want to enjoy the sun but we need to do so in a way that is safe for all."

Health Secretary Matt Hancock also tweeted: "We all want to be outside and enjoying the glorious sunshine but if you are heading out please do it safely and stick to social distancing rules."

The heatwave is set to break with the arrival of thunderstorms bringing lightning strikes and downpours.

Storms had already developed through the course of the day across the north-west of Scotland and are expected to reach much of the west of the UK later on Thursday.

The Met Office said thunderstorms had been recorded across south-west England shortly after 4.30pm.

A yellow weather warning is in place for Northern Ireland, Wales and the west of Scotland and England, with the storms set to move eastwards into Friday.

The rainfall brings a risk of flooding and disruption to some places, the Met Office said.

The National Fire Chiefs Council (NFCC) tweeted: "Although the weather is hot, the water is not. Cold water shock can take your breath away please do not be tempted to cool off in open water and #BeWaterAware."

An amber level three heat-health alert, issued by the Met Office, was extended on Thursday to take in Yorkshire and the east and south of England as well as the West and East Midlands.

Meanwhile, Bournemouth, Christchurch and Poole council said it was left with no choice but to declare a major incident after services were "completely overstretched" as huge numbers of visitors defied advice to stay away during the hot weather in recent days.

Condemning the "irresponsible" behaviour of crowds who gridlocked roads, dumped rubbish, abused refuse collectors and parked illegally, the council said extra police patrols have been brought in.

Health authorities have encouraged those most vulnerable - many of whom have been shielding during lockdown - to protect themselves amid the "exceptionally hot weather forecast this week".

Public Health England (PHE) said older people, those with underlying health conditions, and very young children were all more at risk from the higher temperatures.

The storms are expected to continue from midday on Friday through to Saturday morning, with another yellow warning in place for the whole of the UK.

Areas hit by the storms could experience "torrential downpours" with between 30mm to 50mm of rain falling in an hour.

The Met Office said UV levels were expected to remain at eight across many parts of the UK on Thursday.

Dr Michaela Hegglin, associate professor in atmospheric chemistry at the University of Reading's Department of Meteorology, said Thursday could see some of the "highest UV levels ever recorded" in Britain.

Dog owners have been urged to avoid exercising their pets during the hottest part of the day, with Vets Now, a provider of emergency veterinary care, warning that the average survival rate of a dog diagnosed with heatstroke was 50%.

Meanwhile, the NFCC said it wanted to "debunk this myth" that hand sanitiser left in hot cars could pose a fire risk.

Roy Wilsher, NFCC chair said: "We want to reassure people that this product will not combust if left in a car - even on the hottest day. For hand sanitiser to cause a fire it would need to come into contact with a spark."