An "Arctic trough" is likely to bring thundersnow and gale force winds over the Easter weekend, forecasters say.
By Monday temperatures will struggle to reach double digits, with lows well below freezing.
Parts of the UK saw temperatures reach over 24C on Tuesday, with Kew Gardens in West London leading the way, peaking at 24.5C.
The figure fell just shy of the nation's hottest ever March temperature of 25.6C, which was recorded in 1968 at Mepal in Cambridgeshire.
Sky News weather producer Joanna Robinson said the Easter weekend would start mostly fine but turn "unusually cold" from the north on Sunday.
And the inclement weather will frustrate countless families and groups of friends in England who had been preparing for long-awaited meet-ups with friends.
Easter will mark the first weekend since the rule of six returned outdoors, and officials fear cooler weather could see arranged gatherings move indoors.
Large crowds gathered at parks and beaches during the warm spell earlier in the week, sparking fears the virus could be spread again.
Police have pleaded with people to obey the rules, with the Met saying a tough stance will be taken against any rule-breakers.
"Arctic air will then plunge southwards to affect all areas on Easter Monday, with a significant wind-chill making it feel very cold for early April," she said.
Wintry showers would be fairly widespread and she added: "Thundersnow is possible too - a thunderstorm that occurs with wintry precipitation. It's quite rare.
"The lightning can appear brighter because of the light reflecting off the snowflakes, whereas the sound can be dampened down."
Nicola Maxey, from the Met Office, said parts of the south would be warmer for the longest but the whole country would plummet to single figures by early next week.
Sunny skies are expected across large parts of the country on Friday and Saturday but by Monday the mercury is likely to drop below 10C.
"But it's the colder temperatures that people will remember and note," added Ms Maxey.
"The cold will be with us for much of next week, and with any showers, you could see the possibility of snow falling over the Pennines, Cumbria, Scotland."
Deputy Chief Meteorologist, Mark Sidaway, said: “After a settled, warm spell with plenty of sunshine particularly across England and Wales our weather will take a notable change in direction later in the weekend.
"Very cold Arctic air will move in from the north west through Sunday, bringing snow showers and freezing overnight temperatures.
"The snow showers will predominantly affect the north and west of the UK. The south and east will likely remain drier but still cold with a lower chance of wintry showers.”
Today
Areas of cloud affecting some eastern and central areas, keeping it rather chilly, especially along coasts. Further west, a greater share of sunshine, along with reasonable temperatures, so it should feel fairly warm by afternoon. Breezy in south and east.
Tonight
Still rather cloudy in the east, perhaps an odd light shower along southeastern coasts. Elsewhere dry with clear spells and frost; a few patches of fog, most likely Northern Ireland.
Saturday
Still rather cloudy and chilly in the east and southeast, although a few sunny intervals likely for most. Elsewhere quite sunny; reasonably warm by afternoon, especially across parts of Scotland.
Outlook for Sunday to Tuesday
Fine at first Sunday before a band of rain sweeps south. Much colder with sunshine but hail and snow showers for many follows Monday and Tuesday. Windy, coastal gales.
