28/05/2012 04:51 BST | Updated 28/05/2012 05:35 BST

UK Weather: Britain Set To Cool Off This Week With Thundery Showers On The Way (PICTURES)

Britain will again bask in glorious sunshine today - but it is likely to be the last hurrah before temperatures drop and rain makes an appearance later this week, forecasters said.

Most of the British Isles was bathed in scorching temperatures which reached 27C (80.6F) in places yesterday.

The death of a man who drowned as he rescued two children from the sea was one of a number of water-related tragedies as temperatures soared at the weekend.

But forecasters are predicting a gradual cooling during the week to come, including widespread thundery showers across parts of the country on Wednesday and culminating in a substantially cooler Diamond Jubilee bank holiday weekend.

Forecaster Sally Webb of MeteoGroup, the weather division of the Press Association, said today will be another sunny day across most of the UK but temperatures will be slightly cooler.

Life's a beach - but not for much longer, as the weather is set to turn stormy

She said this cooling trend would accelerate through the week.

"For most areas, tomorrow is going to another sunny day," she said.

"But while it's still going to be warm, we're going to be looking at something like 26C or 27C in London and 24C to 25C elsewhere.

"So it will be a little bit cooler."

Ms Webb said there was chance of thundery showers in some areas of central England but the area which will see the biggest difference will be north-east Scotland, which could be a lot cooler.

She said that by tomorrow a lot of the country would be cooler, especially in the north of England and Scotland.

And by Thursday, top temperatures are likely to be down to 17C or 18C and a similar level is likely to be maintained into the weekend.

Average maximum temperatures for England in May are 14C to 17C (57.2F to 62.6F), while Scotland would normally be between 13C and 15C (55.4F to 59F). Last week was the driest since the end of March, according to the Environment Agency.

Laura Manning, Kelly Sanderson and Rachel Morgan from York play in the sea in Whitby

Several deaths marred the good weather at the weekend.

A 25-year-old man drowned off West Wittering beach, near Chichester, West Sussex, after going to the assistance of two youngsters who were playing in a rubber ring, Sussex Police said.

The news came as police named Nicholas Smith, 23, as the man who died in hospital after getting into difficulty near a waterfall in Linn Park in Glasgow on Saturday.

In a further incident, a 22-year-old man died after getting into difficulty while swimming with friends at a disused quarry at Ballykelly, near Monasterevin, Co Kildare on Saturday night.

A 21-year-old man also died while swimming in a lake in Milton Keynes.

Thames Valley Police said officers were called to the Caldecotte Lake at 6.30pm on Saturday following reports a man had gone missing. Following an extensive search, a body was found just after 11.10am yesterday.

The death of a 15-year-old boy who drowned after he jumped from a bridge into the River Thames in Oxford on Friday night prompted warnings about the dangers of cooling off in rivers.

The body Hussain Mohammed, was not recovered for two hours after he was seen plunging into the water.

In a statement yesterday his family paid tribute to a "happy, cheeky and popular" teenager.

The highest temperatures yesterday were recorded in the south-east and the west of England as well as the north-west of Scotland.

By mid-afternoon, Wisley in Surrey, had the highest temperature at 27.4C (81.3F). Another hot-spot was Porthmadog, in north Wales, which reached 26.9C (80.4F).

Saturday's top spot, Kinlochewe in the Highlands, dipped from the 27.9C (82.2F) reached on Saturday to 25.8C (78.4F).

The sunny weather brought thousands of people out to see the Olympic torch relay today as it passed through south and west Wales.