The capital has enjoyed a scorcher Saturday but temperatures are set to climb even higher on Sunday as a heat health warning is issued.
London is forecast to sizzle at 31C on Sunday, making the hottest place in the UK.
The UK Health and Safety Agency and the Met Office have issued a yellow hot-weather alert from 9am Friday to 9am on Monday, covering most of England.
The warning, which urges people to “watch out for those who might struggle to keep cool in the hot weather”, was issued as temperatures were expected to soar to 32C.
The warning covers London, the South East, South West, East Midlands, West Midlands, east of England, Yorkshire and the Humber.
The Met Office said Sunday in the capital will be largely dry and sunny, with a chance of isolated showers mainly across western and northern areas in the evening.
The city will feel hot and humid, but cooler along the coasts.
The hottest day of the year in the UK so far was June 10, when 32.2C was recorded in Surrey.
Met Office meteorologist Greg Dewhurst Mr Dewhurst said: “If you are outside in the sunshine, stay hydrated and wear sun protection.
“It is also going to be a warm humid night tonight and some people may find it uncomfortable for sleeping.
“The minimum temperatures for most will be the mid to high teens. It will be very warm and humid.
“We will see temperatures rise quite quickly tomorrow in the sunshine and we do need to keep an eye on the risk of thunderstorms as we move to the afternoon and evening, particularly across the north east.”
Temperatures could peak at 32C in the far southeast on Sunday, and into the high 20s elsewhere in the south and east.
In contrast to the sunshine, lightning, hail up to 3cm in diameter and strong, gusty winds could be on the way for some parts.
The Met Office has issued a yellow warning for thunderstorms for parts of northern England and Scotland on Sunday from 1pm-9pm.
These could cause localised flooding. Rainfall will “vary significantly, but some locations could see 30-40mm in 1-2 hours”, according to the forecaster.
London is expected to be the hottest part of the UK, with potential highs of 31C or 32C, but temperatures will be in the high 20s for large parts of England.
The blast of hot weather has come as Glastonbury revellers descended on Worthy Farm in Somerset to watch the likes of Sir Elton John and Guns N’ Roses at the annual festival.
Fresher air is set to move in on Monday, dropping temperatures back down to the low 20s, the Met Office said.
