Two huge regions of high pressure will come together this Friday, bringing tropical air in from Europe and the Azores Islands off the coast of Portugal.
Good Friday is forecast to be the hottest day of the year so far, with temperatures reaching 24C in some parts of the country.
The unexpected heatwave will send the mercury 10C warmer than average for April.
Some parts of the country will bask in almost 10 hours of unbroken sunshine at times this weekend.
Met Office meteorologist Sophie Yeomans said: "Through to the end of the week it is going to get brighter and by Wednesday it will be sunny widely across the UK.
Good Friday shows signs of turning out to be a pretty decent day with temperatures reaching into the 20Cs, it is going to get warmer day by day through the week.
"There is a bit of uncertainty in the forecast for the rest of the weekend but many models are going for warm, dry and sunny weather to hold out with similar temperatures to Friday."
Friday is likely to smash the previous hottest day of the year when 21C was recorded at Kew, London, during a mini heatwave in February.
John Hammond, a meteorologist for online forecasting service Weathertrending, said temperatures will rise steeply from the middle of the week.
“It is going to get warmer day by day through the week”Sophie Yeomans, Met Office meteorologist
He said: "There is going to be quite a transformation in our weather and I suspect by the end of the week I will just be wearing a t-shirt.
"It is going to get a lot warmer at long last, we start the week with easterly winds and we will end the week with easterly winds, the key is the source of the winds by the end of the week, which will be well south across Europe and the Mediterranean, hence that rise in temperatures."
Some long-range forecasters believe this weekend is just the start of a glorious six-week heatwave to come in the run-up to the summer.
The Met Office's 30-day outlook predicts a growing chance of dry, sunny weather through early May, with temperatures unlikely to drop any time soon.
A spokesman said: "On balance, there is a slightly greater chance that some longer dry spells are likely for most places.
"There will however be some brief, more changeable interludes for all parts.
"Temperatures into May will probably be near or slightly above average."
On Monday, Daily Star Online predicted the cold weather to continue until the weekend.