While the warm, dry weather is expected to continue on Wednesday with highs of 22C predicted in some parts, this will quickly fade into unsettled cooler weather in the evening.
Rain and thunderstorms are forecast for the South West, which will then push into south Wales and central southern England into Thursday morning.
The thunderstorms are likely to be accompanied by gusts, fairly large hailstones, torrential rainfall and frequent lightning, the Met Office said.
Forecaster Richard Miles told The Independent: that the weather will turn much cooler towards the weekend, when temperatures could fall below average for the time of year.
"There will be much cooler weather towards the weekend with those heavy showers and possibly thunder on any day between now and Saturday," he said. “It will be less thundery Sunday possibly but really quite cold in the South on Saturday with below average temperatures this weekend.”
Parts of East Anglia, Yorkshire and northwest England could see highs of up to 20/22C on Wednesday, while west Scotland and Northern Ireland could enjoy up to 20C, he added.
However the mercury will drop to 17/18C for most places by Thursday.
“By the weekend at the moment we are looking at low double figures in most places, about 12/13,” he added.
The unsettled weather comes after all four UK nations recorded their hottest ever Easter Monday.
The spring sunshine saw highs of 25C at Heathrow and Northolt, in London, as well as Wisley, in Surrey, beating the previous English record of 24C in the Solent in 2011.
Temperatures reached 24.2C at Kinlochewe in the Scottish Highlands, 23.6C in Cardiff and 21.4C in Armagh.
The highs beat the countries’ previous Easter Monday records of 21.4C at Culzean Castle on Scotland’s Ayrshire coast in 2014, 23.2C in Nantmor in north Wales in 1984, and 21.1C in Northern Ireland’s County Fermanagh in 1984.
Wales, Scotland and Northern Ireland also recorded their highest-ever temperatures for Easter Sunday, the Met Office said.
Temperatures reached 23.4C on Easter Sunday at both Cardiff’s Bute Park, in Wales, and at Scotland’s Royal Botanic Garden Edinburgh, while 21C was recorded at Helen’s Bay in Northern Ireland.