London and other parts of south east England, Cambridgeshire, East Anglia and the Midlands have seen the highest temperatures, while Northern Ireland and western parts of Scotland have missed out on the sunshine.

A Met Office spokesman said: "I think it's squeaked it as the hottest day of the year, although we can't validate it yet.

"It may even have risen a couple of points higher than the 27.8C recorded at the London Weather Centre."

But the heat does not appear to have sent Britons flocking to the coast, according to motoring organisation the RAC.

"The roads have been comparatively quiet," said an RAC spokesman. "People are really thinking about whether their journeys are necessary and trying to economise on fuel while prices are so high."

The good weather is not expected to last until, with thunderstorms forecast for this evening.

John Hutchinson, a forecaster at MeteoGroup, the weather division of the Press Association, said: "There is a risk of some thunderstorms in the South East and up into East Anglia this evening. It's uncertain how many are going to form but when they do there will be torrential downpours."

The rest of the week is expected to see further showers, with a number of tennis matches at Wimbledon likely to be rained off.

"There's certainly going to be rain tomorrow across London and disruption of Wimbledon is highly likely," said the Met Office spokesman.