Borough schoolchildren have been warned against jumping in the Thames from bridges in the borough with thousands getting a day off due to teacher strikes.

The warning comes from the RNLI a year after a 14-year-old boy died after jumping from a bridge at Taggs Island, Hampton.

It comes against the background of a yellow heat alert for London and much of the country from the UK Health Security Agency and the Met Office.

The alert is currently in place from 12 noon today – Friday – and will run through to 9am on Sunday.

The Met Office have forecast temperatures of 27°C to 28°C on Friday and around 30°C on Saturday, while the heatwave is also expected to bring a number of thunderstorms.

Richmond borough has over 20 miles of Thames riverbank and 16 bridges. The bridge at Teddington Lock has been a particular draw for the borough's youngsters in the past.

RNLI's Matt Allchurch issues alert (Credit RNLI Teddington)

Lifeboat Operations Manager at RNLI Teddington, Matt Allchurch, said: "When the weather is warm like it is at the moment there is a temptation to go into the river and we see people jumping off the footbridge

"It's important to know that you don't really know what you are jumping into when you jump from the footbridge.

"There could be all sorts of obstructions under the water, there could be boats passing under just as you jump or other swimmers below you.

"The other danger is cold water shock where the body takes an involuntary inward breath when you jump into cold water and that can result in 2 litres of water in your lungs which is instant drowning.

"If you do survive that, then the secondary measure of cold water shock is the loss of the ability to move your arms and legs because all of the blood from limbs goes into your core to protect your core.

"So we have lost people in the last few years, young people who are good swimmers, trying to swim across the Thames. Even in this warm weather we are having at the moment the Thames is really quite cold.

"If you are going to use the river, stay close to the edge in shallow water."

Jumping into Thames can trigger 'cold water shock'

Head of Extreme Events and Health Protection at UKHSA, Dr Agostinho Sousa, said: "This weekend it's important that everyone takes sensible precautions while enjoying the sun.

"The forecasted high temperatures are expected to be short lived, but could primarily impact those over the age of 65 or those with pre-existing health conditions. If you have friends, family or neighbours who are more vulnerable, it is important to check in on them and ensure they are aware of the forecasts and are following the necessary advice."

Met Office Deputy Chief Meteorologist Dan Harris said: "Temperatures will be on the rise from Friday, with a plume of continental air allowing temperatures to reach, and perhaps locally exceed, 30°C in parts of England on Friday and Saturday. In addition, temperatures overnight will remain high, especially in towns and cities, which will make for an uncomfortably warm night for some.

"Temperatures are likely to start to drop from the west on Saturday and more widely into Sunday, as showers and thunderstorms sweep northeast across the country."