THE Met Office has this morning issued a severe weather warning for the Westcountry.

The Exeter-based weather agency has warned motorists to be aware of " very heavy, thundery rain in Cornwall and Devon" for much of the day.

The alerts comes as it confirmed heatwave conditions across parts of the UK yesterday as the country continued to swelter.

And while the Westcountry avoided the extremes of heat felt elsewhere, the agency said that "very heavy, thundery rain moving slowly northeastwards" during the day with brighter spells in the late afternoon.

"Further thunderstorms will affect parts of southwest England during the day and these will give accumulations of more than 15 mm in 3 hours in places, before gradually clearing away eastwards," the Met Office said this morning. "The public are advised to take extra care and refer to the Highways Agency for further advice on traffic disruption on motorways and trunk roads."

The Met Office warning was issued for both Devon and Cornwall and is timed from 8.35am to 5pm.

Meanwhile, the organisation raised the Heat-Health Watch to level three for London and South East England yesterday morning.

The South West is currently at level one of four on the heatwave plan – the minimum state of vigilance during the summer.

Level three is described as "heatwave action", while level four is "emergency", where there is a risk that death and illness may occur among the fit and healthy, rather than just high-risk groups.

London and the South East have seen temperatures climb to highs of about 31C.

It prompted the Government to set up a heatwave advice page on its Directgov website as NHS Direct received 309 calls on Monday about the heat. However, most of these calls were regarding insect bites rather than heatstroke.

The last month has been the hottest, driest and sunniest since July 2006, which was the last time the Met Office confirmed heatwave conditions.

Urban areas have suffered worst from the current spell of hot weather, forecaster Sarah Holland said, while the largely rural Westcountry has escaped the worst of the unbearable heat thanks to its sea breezes and open countryside.

However, she said people should still be aware that temperatures in the region are "very warm".

Yesterday temperatures of about 24C were recorded around Bodmin, Plymouth and Camborne, while further inland temperatures reached about 27C.

Ms Holland said: "People need to make sure they drink lots of fluids – particularly the elderly and the vulnerable."

She also advised keeping curtains and windows closed during the day if possible, and opening them at night.

Official heatwave advice from Wayne Elliott, head of health forecasting at the Met Office, is to stay out of the heat during the middle of the day; stay cool and look out for others, especially older people, those living alone and babies and children.

Temperatures were expected to peak yesterday and today and the country can then look forward to "fresher" weather – and rain. Heavy downpours are expected to move across the South West this morning, with up to 50mm (about two inches) of rain falling in some places.