Parts of southern England have had only 6% of normal rainfall so far this summer

This article is more than 2 years old

This article is more than 2 years old

Parts of Britain are forecast to reach temperatures of 36C (95F) this week before thunderstorms, hail and strong winds take hold.

After weeks without rain, torrential downpours are forecast to hit parts of the UK on Friday, with as much as 30mm (1in) expected to fall in an hour. The Met Office has issued a thunderstorm warning from Friday afternoon covering the north and east of England.

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A temperature of 33.3C was recorded at Santon Downham, in Suffolk, on Monday, the hottest day of the year so far. Temperatures were around 21C in parts of East Anglia and London past midnight.

Forecasters expect the prolonged heatwave to continue, with temperatures set to peak on Thursday and Friday.

Becky Mitchell, a Met Office meteorologist, said the high temperatures were a result of warm air coming up from France combined with high pressure across the country.

An amber “heat health watch” warning was issued for parts of England, with people advised to stay out of the sun for the remainder of the working week. An amber or level-three warning is issued when temperatures are predicted to hit 30C during the day and 15C at night for at least two consecutive days.

The warning that there was a 90% possibility of heatwave conditions came into force on Monday morning and will last until 9am on Friday in the Midlands, south-east England and eastern England.

The Society of Acute Medicine raised concerns about patients and staff in overheated hospitals. Dr Nick Scriven, the society’s president, said most hospitals were designed to keep patients warm all year round but could become too hot in such high temperatures.

The Royal College of Nursing raised concerns that some nurses were unable to stay properly hydrated during their shifts as they were not allowed to take water bottles on to wards.

The hottest July temperature on record is 36.7C, at Heathrow on 1 July 2015.

Several places have now had 54 consecutive dry days – meaning less than 1mm of rain – stretching back to 30 May, the longest spell since 1969 when 70 days passed with no significant rainfall, according to the Met Office.

The longest run of days with no rain at all this summer is 48 at Brooms Barn, near Bury St Edmunds.

A Met Office spokesman said: “For the UK as a whole we’ve only seen about 20% of the rainfall we’d normally expect throughout the whole summer. Parts of southern England have seen only 6%.”

Businesses are being urged to relax dress codes and keep offices cool in order to help employees cope with the heatwave. The TUC suggested allowing staff to work flexible hours to avoid travelling at peak times and letting workers wear lightweight clothes.

There are no legal restrictions for when the workplace becomes too hot. The TUC has been campaigning for a change in the law to introduce a new maximum indoor temperature of 30C, or 27C for those doing strenuous jobs.

Frances O’Grady, the union’s general secretary, said: “It’s no fun working in a baking office or factory.” She urged employers to do all they could to keep temperatures down.