Britain will be warmer than Marbella and Ibiza with highs of 27C set to smash this year's current recorded hottest day.
BBC forecaster Darren Bett said large parts of the UK will be getting "much warmer" this week, with temperatures likely to peak on Wednesday.
The current hottest day so far in 2020 was 26C on April 10 in Treknow, Cornwall.
Mr Bett said Monday, meanwhile, could reach 24C in London and 25C tomorrow but warned rain will likely strike in the north-west as a "conveyor belt of moisture" moves in.
"The peak of the heat is likely to be on Wednesday, unless you're in the northern isles where we've got cloud and to start with some outbreaks of rain.
"Otherwise it's going to be dry and more sunshine widely thanks to that southerly breeze - that will push the temperatures up into Scotland into the low 20s."
However, he said "things start to break down on Thursday" as more rain makes its way from the west, with potentially heavy and thundery showers.
But the mini heatwave will continue into Friday for some, testing the nation's resolve as people are asked to avoid crowded outdoor spaces so two metre social distancing can be observed.
Met Office forecaster Matthew Box said: "It's going to be very hot for large parts of England for most of the week, reaching highs of 27C on Wednesday, which would make it the hottest day of the year so far.
"This will occur due to large areas of high pressure, combined with southerly winds from the continent, bringing with it, pleasant sunshine, dry skies and warmer air."
He added there is a possibility of thunder and bands of rain across the south and east of England and Wales on Thursday while Friday could be windy, mainly for western areas, with heavy downpours.
UK 5 day weather forecast
Today:
A good deal of cloud across central and northern areas, with some rain or drizzle at times, although becoming dry with sunny spells over many parts of Scotland during the afternoon. Southern parts dry and warm with sunny spells.
Tonight:
Clear spells and patchy mist and fog in the south, else rather cloudy central and northern areas with some rain or drizzle, chiefly in areas exposed to the west.
Tuesday:
Early mist and low cloud in south clearing to leave sunny periods, and becoming locally very warm in south-east England. Cloudier further north and west with some rain/drizzle in places.
Outlook for Wednesday to Friday:
Sunny and very warm inland on Wednesday, although cooler with low cloud around some coasts. Turning generally cooler and more unsettled thereafter with showers, thunderstorms and rain at times.
