Last month was the warmest April in the UK on record, with virtually no rain in some areas, the Met Office said.
Runners in the London Marathon sweltered in the heat
The average temperature was 10.2C (50.4F), beating the previous April high of 9.2C (48.6F), recorded in 1943.
Rainfall in the driest region, East Anglia, was only 5% of the expected amount, and even in the wettest parts of Scotland it was down 30%.
BBC forecaster Tomasz Schafernaker said it had been an "absolutely incredible" month across the whole of the UK.
The mean temperature of 10.2C was 3.3C higher than the long-term average of 6.9C (44.4F) recorded throughout the period of 1971 to 2000.
'Normal for July'
Mr Schafernaker said figures so much above the average were "almost unheard of".
The maximum on any one day was 26.5C (79.7F) in East Sussex, "a normal July temperature", he added.
Sunshine hours were also as much as 50% higher than average across England, Wales, Scotland and Northern Ireland.
Meteorologists had said they expected this April to be the warmest in central England for more than 300 years.
Met Office forecaster John Hammond said: "This has been the warmest April on record and certainly one of the driest."
In Suffolk, England's most easterly county, there was just 2.6mm of rain, compared with the normal monthly average of 44.2mm.
The warm weather at the end of the month prompted the Department for Environment, Food and Rural Affairs (Defra) to issue its first "summer smog" warning for 2007.
'Desperate for farmers'
Mr Hammond said the unseasonal heat and drought was causing major problems for farmers and growers, especially in the east of England.
"I understand that growth is stalling because there has been no rain," he said.
"They're desperate for some rain."
He added that May had started off with more of the same dry, warm conditions, but a spell of wetter weather was possible from the end of next weekend.