Temperatures in Britain hit 30C for the first time this year but parts of the country are also set to be hit by thunderstorms.
The Met Office said the highest temperature so far on Saturday was 30.5C, which was recorded at Heathrow Airport on Saturday, but some other parts of the south-east also reached the 30C.
It added that temperatures could reach 32C by the end of the day.
However, a yellow thunderstorm warning was issued for Wales and much of southern and central England before 9pm on Saturday, highlighting potential travel disruptions, power outages and localized flooding.
A second amber warning for thunder and lightning will be issued for Wales, Northern Ireland and much of western and central England, as well as Scotland, from noon to 9pm on Sunday.
Parts of eastern and northern Scotland may avoid the most extreme conditions.
Dan Stroud, a meteorologist at the Met Office, said: “There will be more clouds on Sunday and the temperature will drop a little bit, but it will still be 28 or 29C, triggering a few showers and thunderstorm warnings.
“The beginning of next week will be a continuation of the hot weather. There will be thunder, showers on Monday, but then the weather will stabilize on Tuesday and mid-week.
“But it’s going to keep this well above average. Much of the UK will meet the heatwave criteria.”
The UK Health Security Agency (UKHSA) has issued a yellow heat weather alert until 9am on Tuesday for the West Midlands, East Midlands, East, South East and South West of England.
This means that the effects of heat “could affect the entire health service … and the wider population, not just the most vulnerable”.
Another, less severe yellow alert warning of some disruption to services due to weather conditions is in place for the northeast, northwest and Yorkshire and Humber regions of England, as well as London.
