As seaside resorts filled with day trippers, forecasters said the weather was expected to be just as hot today. But coastguards warned people to be prepared for low temperatures in the sea, which has not yet had time to warm up.
Gerry Wood, of Falmouth Coastguard, said: "The sea is still very cold and can catch people unawares. Despite the warm weather, the sea demands respect as prolonged immersion in sea water can cause hypothermia."
A spokesman for the London Weather Centre said it was likely to be the third hottest May Day since the holiday was created 21 years ago.
"The May bank holiday started in 1978. For ages and ages, it was a byword for cold and rain," he said.
"The first one we had, it chucked it down, with the exception of Scotland where it wasn't a bank holiday.
"We had to wait until 1990 for the first really hot one and we have only had two which are better than the one we are having now."
The prospect of good weather will cheer the owners of tourist attractions where takings fell last year because of the low temperatures, strong pound and the World Cup.
The number of visitors to many of the country's most popular sites dropped for the first time in seven years, figures from the UK's four national tourist boards showed.
Alton Towers was the most popular of the admission-charging attractions ousting Madame Tussauds, but visits to leisure parks fell by 3 per cent and to historic properties by 1 per cent. Blackpool Pleasure Beach was the most popular free attraction, with an estimated 7.1 million visitors.
"The poor summer weather, the strong pound and football World Cup all had a negative impact on visits," said the English Tourist Board.Reuse content