Four people have drowned as Britain continues to swelter during the hottest spell of weather for seven years.
Yesterday was the hottest day of the year so far in Britain.
Temperatures reached 32.2C (90F) at Hampton in Surrey yesterday afternoon, making it the warmest weather since Saturday, when a high of 31.4C (88.5F) was recorded at Heathrow Airport.
A level three heat health watch is in place for London and the South East with the elderly and young, and those with chronic health conditions, urged to take extra care.
Meanwhile, police and fire chiefs reiterated warnings about escaping the heat by swimming in open water after four people died at lakes in Norfolk, a river on the Shropshire/North Wales border and the sea in Cornwall.
Forecasters said Britain was in the midst of its first prolonged heatwave since 2006 and predicted that the record for the warmest day of the year could be broken again, with temperatures as high as 32C (89.7F) in parts of England yesterday.
A 16-year-old boy and a 41-year-old man from King's Lynn were found dead in separate lakes at Bawsey Pits, Norfolk, on Tuesday night.
It is believed the man had swum about 50 yards (45m) out in one of the flooded quarries towards an island when he disappeared below the water.
In an unrelated incident, the teenager was reported missing at another lake about half-a-mile away.
And a man died after getting into difficulties near the confluence of the Rivers Dee and Ceiriog on the Shropshire/North Wales border.
Believed to be a 21-year-old from Shropshire, he was airlifted to the Royal Shrewsbury Hospital but emergency services were unable to save his life.
Meanwhile, a 40-year-old woman from Saltash died swimming in the sea at Seaton, near Torpoint in Cornwall.
Police said she had suffered a "medical episode" and was pulled from the water by an off-duty officer.
With the mercury showing no signs of falling, Gemma Plumb, a forecaster with MeteoGroup said: "There is no proper definition of heatwave in the UK but we are undoubtedly in the midst of one now.
"It is the longest period of hot weather since 2006, with prolonged temperatures above the average for the time of year."