As thunderstorms hit some parts of the country, the Department of Health warned people to take precautions against the scorching heat. The elderly, the young and the chronically ill are most at risk.

The heatwave is expected to hit London, the South East and the West Midlands hardest.

Forecasters say that temperatures could peak at 33C in some areas — hotter than on June 12, when temperatures reached 32.4C in London.

It is due to turn cooler towards the end of the week, with thunderstorms spreading across the country.

High temperatures can cause heat exhaustion and heat stroke, which can be fatal.

The Department of Health has advised that anyone who experiences symptoms of heat exhaustion, including headaches, dizziness, nausea and vomiting, should take a lukewarm shower or sponge themselves with cold water.

The advice is to keep out of the sun, particularly from 11am to 4pm, and to drink plenty of liquids. Alcohol, tea and coffee should be avoided as they worsen dehydration.

Parents should ensure that their children are covered in protective clothing, such as long-sleeved tops and hats, as well as a high-factor sunscreen.

“It’s going to get very, very hot,” a spokesman for the Met Office said. “June was a sunny, dry month and this will continue over the next week.

“While most people can cope in such conditions, it can be dangerous for older people and children, who should take particular precautions and try to avoid the sun.”

The heatwave warning follows one of the hottest months in recent times. The average temperature in June — taking both days and nights into account — was 19.1C.

In 2003 about 27,000 people across Europe died from the heat. The number of people aged over 75 who died in London that summer rose by 60 per cent.

Temperatures in Northern Ireland this June surpassed those in 2003, with an average of 18.7C compared with 17.7C three years ago.

Yesterday thunder and lightning struck the south coast, leading to a four-hour storm that set off car alarms. In Devon, Paul Sharp, 24, said: “I was out really early in the morning and the storm was incredible. The rain was torrential, but it was still really warm — and the thunder was the loudest I’ve ever heard.”

Manchester was hit by torrential downpours and flash flooding. The flight carrying England’s footballers back from Stansted, where they had arrived from Germany, had to be diverted from Manchester to Liverpool airport while two lanes of the M60 were also closed.

Elsewhere in the city, a small number of houses had to be evacuated while a 90-year-old man was among six people rescued from their cars by firefighters after they became trapped in 4ft-deep water.

In Aberdeen rain lashed the city and power cuts occurred in more than 550 homes. Roads were severely affected.

The Met spokesman said that the blustery weather would cool temperatures somewhat, but that it would remain hot and become humid.

He said that westerly and northern areas were the most likely to be affected by storms, although other regions could be hit later in the week.

However much an inconvenience, the rain will come as a blessing to homeowners whose gardens have suffered from one of the driest summers in years.

Met Office figures show that the UK rainfall in June was 38.4mm, only 54 per cent of the long-term average, while in England alone it was lower still at 22.8mm — 38 per cent of the average.

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