Health warnings issued with three-day ‘heatwave’ set to hit the UK

However, the highest temperatures are likely to fall short of mid-July's year-high of 33.5C as Spanish plume shifts course

Sunbathers enjoy the hot weather in St James' Park in central London (PA)

Britons are set to bask in a three-day sunny spell as the mercury rises well above average for the time of year. The week is getting off to a warm start with most of the UK forecast to enjoy some summer sun.

The south-west will see highs of 28C (82F) on Tuesday, while other areas can expect to experience temperatures in the low to mid-20s. A wave of hot air – known as a Spanish plume – was expected to sweep across the UK from Spain but a change in direction means the predicted highs of 30C (86F) and above are unlikely, the Met Office said.

The air, now expected to come from the south-east rather than the south, will be less humid, meteorologist Alex Burkill said.

“It will still be above average for the time of year. It will definitely feel like summer, perhaps just not as hot as we thought it would be," he said.

Temperatures will fall short of mid-July's year-high of 33.5C (92F).

Warning sunseekers to be careful when out and about in hot weather, St John Ambulance advised people to keep in the shade where possible, stay hydrated and wear sun cream.

Training officer Clive James said: “The classic signs of heat exhaustion and heatstroke are dizziness and headache – if you're suffering from either, find somewhere cool and drink plenty of fluids.

"If your symptoms don't get any better and you're concerned, seek medical attention.”

Mr Burkill reassured those worried about trying to sleep through muggy nights.

“It is likely to be quite chilly overnight, with temperatures falling to single figures in some places. It could be around 3C or 4C (39F) in parts of Scotland,” he said.

The good weather is not expected to last long as unsettled conditions are in-store for Thursday and into the weekend.

PA