London-based The Connection at St Martin’s said that being homeless in this extreme weather is as dangerous as in winter and has launched an emergency hot weather appeal.

It comes as the Met Office forecast today could be the hottest July day ever in the capital with temperatures soaring as high as 37C.

The St Martin’s street team has been out daily, handing bottles of water and sun protection to homeless people and advising them how to stay safe.

A spokeswoman said: “We are seeing people wearing the same clothes that they wear every day: thick jumpers and coats which are not suitable for this weather. They are still carrying their lives around on their backs as they have nowhere to store their belongings. This puts people at very serious risk of becoming dangerously dehydrated and getting sun stroke, which if not addressed quickly can leave people unconscious, and even at risk of dying.

“Rough sleepers with alcohol or substance misuse problems are even more vulnerable from exposure to the sun because these exacerbate dehydration. We are taking extra care to help these people. We’re also seeing people with serious burns on their body and working with medical teams to help people get the right treatment.”

The charity is requesting donations of £8 to buy a Stay Cool kit so people are protected from the sun.