Sadiq Khan has activated a severe weather emergency response in the capital to help rough sleepers as temperatures nudge 36C in the heatwave.
On the London mayor’s orders all boroughs and homeless services will be asked to conduct welfare checks on vulnerable people.
They will also provide sunscreen, water and information about staying safe in the extreme heat.
Emergency responses are usually triggered in winter when temperatures plummet.
Mr Khan said: "This ongoing heatwave could be dangerous for anyone, but for people sleeping rough, there are additional risks.
"Across the capital, we are taking action to assist those forced to sleep rough in these extremely high temperatures, by increasing welfare checks, providing plenty of water and sunscreen, and ensuring people sleeping rough know where to access cool spaces and water fountains."
The mercury is set to increase to even higher temperatures this week ahead of this weekend when the Met Office has ordered an amber heat warning for swathes of the nation.
Earlier today it was extended from Sunday into the following Tuesday as there is a “danger to life or potential serious illness, with adverse health effects likely across the population.”
In response Downing Street has refused to rule out a national heatwave emergency.
No10 said there are no plans “at the moment” for nationwide measures, despite a COBRA meeting on Monday to decide whether to declare the first-ever national heatwave emergency.
Boris Johnson ’s official spokesman said: “There will be further coordination meetings throughout the week.
“It’s up to UKHSA [the UK Health Security Agency] and the Met [Office] to decide whether to move further.
“But as it stands there are health alerts for the majority of the country because we expect temperatures to remain high. Advice has been issued already both to the general public and to the NHS.
“At the moment there are no plans to issue national-wide measures but we will wait for further advice from experts like UKHSA and the Met on what the coming days will bring.
“There is already advice for the public which we encourage people to look up.”
Forecasters believe there is a 30% chance the mercury could surpass the current UK record of 38.7C, set in Cambridge in 2019, as the Met Office predicts temperatures "in excess of 35C" in the southeast.
There could also be road closures, and delays and cancellations to rail and air travel, while ambulance services in England are on the highest level of alert as difficulties with the hot weather combine with Covid absences among staff and ongoing delays handing patients over to A&E.
Forecaster Matthew Box said: "As we get into Sunday it looks like we could see temperatures rise into the high 20s and into the low 30s as well but potentially a few spots getting 34C or 35C by Sunday and probably the same again on Monday.
"We could see by Monday temperatures getting towards the mid or high 30s and there's about a 30% chance we could see the UK record broken, most likely on Monday at the moment."
