Sunshine could give way to snow as warmer weather is due to linger across Britain only until Sunday.
This week's mild temperatures will be replaced by chilly lows and the possibility of snow from Monday, forecasters warned.
On Tuesday Britain basked in sunshine, enjoying highs of 17.5 degrees in Trawsgoed, Wales, 17.1 degrees in Gravesend, Kent, and 17 degrees in central London.
Temperatures were up to seven degrees higher than average for this time of year across Britain.
Today the temperature will hover at around 14 degrees in England and Wales and at around seven degrees in Scotland and Northern Ireland, before dropping a few more degrees throughout the rest of the week.
However, winter will prove it has not quite departed by bringing back the possibility of snow next week.
Brendan Jones, a forecaster for MeteoGroup, the weather division of the Press Association, said: "Yesterday was significantly warmer than average.
"We won't see these temperatures again this week, but nevertheless it will stay pretty mild this week, with above-average temperatures.
"Most of us will see some rain this week, making it a little unsettled.
"But from Sunday there will be a return of cold weather starting in Scotland and spreading to all areas by Monday.
"There could even be the chance of snow on Monday and Wednesday - all areas should be on alert for at least a little bit of snow."
He added that it is not unusual for Britain to see snow in March and though we have technically entered Spring, the weather tends to be no different to February.