© Manchester Evening News SyndicationChildren cooling off in the fountains at Piccadilly Gardens in Manchester.
An official heatwave is likely to be declared in Britain today, with temperatures in the south likely to hit 33C (91.4F) later this week.

If officials raise the threat level from amber to red, measures including putting social services and hospitals on alert for a wave of casualties of scorching days and sleepless nights will come in to force.

Temperatures on the outskirts of London hit 30C yesterday, remained in the low 20s overnight in some areas and are expected to top that today.

Torrential downpours have been predicted to hit the north, along with scattered thundery showers in the south, but without any relief from the heat until the weekend.

Declaration of a heatwave would reflect an official forecast that the weather will be hot enough for at least two consecutive days to cause major health problems for many people.

The hottest spell in almost two years is already leaving the elderly, very young, frail and those with breathing problems particularly vulnerable.

During record temperatures in 2003, an estimated 2,000 people died from heat-related conditions.

NHS Direct and the London Ambulance Service, which will bear the brunt of pressure in the capital, are gearing up for a major demand on their services.

The UK's heatwave plan remains at level two, but the Met Office believes it will be raised to level three.

Official advice says anyone who can should stay indoors from noon to 3pm, draw curtains to shade rooms, drink plenty of water and wear sunscreen while outdoors.

Many schools are already keeping children out of playgrounds during breaktimes.

Care homes have been advised to monitor indoor temperatures four times a day, identify high-risk residents and prepare a cool room.

Officials are urging people to identify the coolest room in their home, stock up on essential supplies to cut down on shopping trips and check on neighbours, relatives and friends, especially those with mobility problems.

The department of health and the lifeboat service have warned people to be careful if going swimming.

A teenage boy who has not yet been formally identified, was drowned while swimming with three friends in the River Severn yesterday.

Search teams using a helicopter and boat recovered the boy's body. He was confirmed dead on arrival at the Worcestershire Royal hospital.