Scientists from Imperial College London say that in the most vulnerable districts, in London and the southeast, the odds of dying from heart or lung causes increased by more than 10 per cent for every 1C rise in temperature.
Those most at risk areas include more deprived districts of London such as Hackney and Tower Hamlets, with the odds of dying more than doubling on very hot days.
London is set to bask in the highest temperatures of the year so far todayRead the full story ›
When the sun comes out, Londoners head to the parks by the thousand.
But all that extra use has taken its toll on the Royal Parks deckchairs, and there's more hot weather on the way, so 6,720 of them will have their old canvas stripped and recycled into reusable bags. .
That means two miles (4,700 metres) of new canvas has had to be ordered. Enough to stretch from Buckingham Palace to Primrose Hill.
In the last couple of hours the Met Office has advised that it is likely to downgrade its heatwave warning from level 3 to level 2 over the weekend as temperatures are dropping - but it could well be raised again next week as temperatures rise again.
Mertin Stew reports:
The heatwave is taking its toll of London's emergency services. With no let-up in the soaring temperatures, firefighters and paramedics have seen a surge in calls.
And as Londoners heed advice about coping with the heat, Thames Water said it has seen a 15% rise in the demand for tap water in the capital. Piers Hopkirk reports:
Ambulance crews are struggling to cope in the heatwave as they try to rescue people in "dangerously high" temperatures.
Paramedic Karl Paddison warned that even healthy people can fall foul of hot sun, adding that the London Ambulance Service has to attend to people who have collapsed on a daily basis.
And the the worst effects are being felt by people stuck in lifts, in the capital's Underground, or those who are so burned they have to be admitted to A&E with sun stroke.
Mervyn Kohler, special adviser to charity Age UK has told ITV London that heat can be "stressful" for older people, as scorching temperature continue across the UK.
Mr Kohler said: "For God's sake, let's enjoy it, you have to act sensibly and responsibly, and enjoy the warm weather".