Scotland will see the mercury rise to as high as 23C (74.3F), although cloud coverage will keep temperatures slightly cooler than other parts of the UK.
Glasgow looks set to reach 23C later this week while Edinburgh is also expected to heat up to a maximum of 22C.
Aberdeen and Dundee will both hit a pleasant 21C on Wednesday and Thursday respectively.
Much of England and Wales will also enjoy temperatures in the 20s, with only the odd shower predicted in the west of the country.
Alex Burkill, meteorologist at the Exeter-based Met Office, said: “Monday is looking like a pretty good day across much of the country, with a good deal of sunshine.
“We could see highs of 25C (77F) in London, the East Midlands and East Anglia, which will get the best of the weather.
“There will be some patchy drizzle on Tuesday and Wednesday when temperatures dip a couple of degrees maybe, but by Thursday we expect to see things on the rise again.
“If we reach 26C (78.8F) then we will have the hottest day of the year so far, but it is Friday which is shaping up to see temperatures peaking.
“We are looking at the high 20s - possibly 27C - with warm air coming up from the south. It’s going to feel pretty good.”
But those looking for the warm run to continue into the forthcoming Bank Holiday weekend might be left disappointed.
Mr Burkill said: “This is looking like being the warmest spell we’ve had since September last year, but it might not last beyond Friday - from then we are looking at the possibility of some thunder and showers and temperatures taking a dip.”