The working week will be book-ended by the best of the weather, with highs of up to 25C expected in Yorkshire on Friday.
Much of England and Wales will enjoy temperatures in the 20s throughout the week, with only the odd shower predicted in the west of the country.
Scotland and Northern Ireland will also see the mercury rise in the next week, although cloud coverage is expected to keep temperatures slightly cooler.
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.
"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."
The Met Office's forecast for Yorkshire:
Any patches of low cloud should soon clear leaving Sunday a fine and dry day with some sunny spells, although some cloud will build up by the afternoon. Feeling warm in the sunshine. Maximum temperature 18 °C.
Remaining fine and dry through the night. Some cloud around at first but soon becoming largly clear with perhaps a few mist patches forming in places. Minimum temperature 8 °C.
After a bright and sunny start, cloud will tend to increase through the day. Most places remaining dry but the odd shower is possible in the north later. Feeling warm. Maximum temperature 21 °C.
Outlook for Tuesday to Thursday:
Fine and dry throughout the outlook period with sunny spells and generally light winds and becoming very warm in places by Thursday.