July has been the hottest month since records began in 1914, according to Met Office figures.
Britons have basked in record temperatures during the heatwave
Provisional statistics show the average night and day temperature during the month was 17.8C (64.04F).
The previous record for a whole month was 17.3C (63.14F), which was set in July 1983 and August 1995.
A Met Office spokesman said: "These dramatic figures for the whole month show how widespread and long-lasting the heatwave has been this summer."
The heatwave has brought various problems around the UK.
It was blamed for power cuts in central London, where customers were urged to switch off air-conditioning to reduce electricity demand.
The harvest is thought to have been the earliest since 1976, which has led to warnings of shortages of vegetables in the shops and higher prices.
The hottest single day during the month was at Wisley, Surrey, where temperatures reached 36.5C (97.7F) on 19 July.
Temperatures are forecast to hit a maximum of 24C (75F), in London, during the rest of the week.