Temperatures could reach up to 10C above average in England and Wales next week
London Marathon runners could enjoy highs of 22C in the capital on Sunday.
Temperatures could reach up to 10C above average across most of England and Wales on Tuesday, the Met Office has said.
It is possible that top temperatures could reach 23C or 24C, but the nights will still be cold at about 4C-7C.
A “large chunk” of England could be enjoying these temperatures which would be “very warm for the time of year”, according to Met Office meteorologist Simon Partridge.
He said: “The average temperature for this time of year is about 13C to 14C, so for a lot of central and south-eastern England on Monday and Tuesday, there is quite possibly the chance that we will see temperatures around the low to mid 20s in the early part of the week.
“Certainly on Monday and Tuesday, the potential 23C is pretty high with a with a small chance of seeing 24C – but even 23C for parts of the Midlands would put them 10C above average for the time of year.
“There’s a pretty good chance of seeing that early next week, which is obviously very warm for the time of year.
“Obviously, 23C is not record breaking in terms of absolute temperatures, but for the end of April, that is well above average.”
It looks like Sunday’s London Marathon runners will have to endure temperatures of 21C to 22C as they try to complete the 26.2 mile course.
Some 56,000 people are expected to tackle the route in what is the 45th edition of the event.
It could enter the record books as the largest marathon in the world if the number of finishers surpasses the 55,646 who completed the New York Marathon in November.
The TCS Mini London Marathon will also take place on Saturday, with about 17,000 children due to run, jog, walk, or wheel one mile (1.6 kilometres).
A warm spell of weather is expected to start on Sunday before forecasts become a little bit sketchy as there is potential for a lot of cloud to come in from either the north or south.
Mr Partridge added: “Typically for people that are running the marathon, that (warm weather) kicks in on the wrong day.
“For those guys, they probably would have rather run the day before when it would be be three or four degrees cooler.”
Saturday will likely see patchy rain initially moving east across most of Scotland, England and Wales, with brighter conditions further north before sunny spells develop more widely into the afternoon.
Temperatures will stay around average with highs of 18C but may start to rise as the weekend progresses, particularly on Sunday.
While northern regions of the UK will continue to see some cloud and scattered showers on Monday, the rest of the country will stay dry and bright with temperatures of up to 24C in the South East.
