UK weather forecast latest: London Marathon runners face hottest race ever... as flash floods hit UK

This year's London Marathon looks set to be the hottest on record while elsewhere in the country flash flooding will bring the glorious heatwave to an abrupt end.

Runners could be provided some “light relief” as rain showers roll over the capital on Sunday, but forecasters have warned them not to over exert themselves as temperatures look set to reach between 22 and 23C.

The UK faces a period of transition this weekend as record breaking temperatures fall back down to “normal levels for April," forecasters said.

The Met Office has issued a weather warning for Saturday afternoon in the north of England and Wales as thunderstorms are expected to cause the potential risk of flash flooding.

These showers are expected to move north eastwards overnight and in some places could bring hail and gusty winds.

Forecasters predict 15 and 30 mm of rain will fall and anticipate lightning in some parts.

While thunderstorms are not expected in the capital on Sunday, marathon runners will face some showery spells.

“This could make conditions dreary for spectators but will provide a welcome relief to runners,” Grahame Madge, a spokesman for the Met Office said.

The hottest races on record was in 1996 and 2007, where runners endured temperatures of 22.2C during the 26-mile run.

But Mr Madge said there is the potential for this years’ race to be even hotter as the mercury level climbs towards 23C.

He said: "A big caveat here is obviously a weather station temperature record will feel a bit different to what it might feel like trackside where you have the warmth coming up from the tarmac and other people.

"Trackside temperatures will probably feel even warmer than that, so the advice to runners is to look at the forecast and prepare for the fact that this could be one of the warmer marathons."

Moving into next week, cooler temperatures are expected across the country as weather moves in from the Atlantic.

“Temperature levels will return to normal for April with showers and brighter spells expected” said Mr Madge.

Tens of thousands of runners are expected to take part in the arduous feat as they pound the course around much of London, cheered on by thousands of supporters.

Race organisers have announced they will add more water, ice and shower stations along the 26.2-mile route so participants can cool down in the heat.

Conditions may also be especially difficult for fancy-dress runners, including the almost 100 attempting Guinness World Records dressed in outfits such as a suit of armour, a Paddington Bear costume and ski boots.

And runners have been advised to consider dropping their goal times and to run more slowly, to apply suncream and to wear lightweight clothing for warmer conditions.

Mr Madge said Sunday will start off bright, with potentially some higher cloud which "may reduce the extreme glare", but warned that later on there could be some downpours due to "increasingly humid air".

Set to increase in intensity and frequency throughout the event, he said the showers should bring respite for participants, but may not be so enjoyable for the spectators.

Brits will also be able to enjoy the Lyrid meteor shower over the weekend.

Astronomers said hundreds of meteors with long, glowing tails will streak across the sky in a display that will reach its peak in London early on Sunday morning.