Public health officials say at least 650 people have died from the sweltering temperatures, which peaked at 90 degrees Wednesday, The Daily Telegraph reported.
British researchers estimated Thursday the heat had killed as many as 780 people.
At least 14 people have died in water-related deaths as Britons fled to rivers, lakes and the seashore to escape the longest heat wave in seven years.
A Met Office forecaster said temperatures could reach 95 degrees next week.
A newly resurfaced road in the center of Cambridge melted in the heat, with the asphalt settling like a wave at the edge of the road.
Firefighters have battled about 21 wildfires a day in July, and crops such as wheat and winter barley that are almost ready for harvest are considered particularly vulnerable.
Wildfires ripped through valleys in South Wales Thursday night, while fighters in Scotland battled large-scale blazes in Tentsmuir Forest, The Times of London reported.
London has reported 1,000 grass fires this summer.
Meteorologists cautioned farmers to be on high alert this weekend as the heat wave went on unabated, putting crops across the country at risk, The Independent reported.