March was the sunniest month since 1929, and the warmest since 1997 according to forecasters.
But the the warm weather will not last into April, the Met Office said - and they even predicted snow by Tuesday evening.
Up to 10cm of snow is predicted for the Highlands of Scotland, and sleet could be seen further south.
Travel disruption is also predicted in northern England after two severe weather warnings were released.
The Met Office said the cold weather will sweep into the UK from Norway and Sweden.
Temperatures could fall as low as -5C or -6C in the north, and some snow could even be seen in the south as the cold air drifts across the country, but is not likely to settle.
The cold will likely come as a shock after an extremely dry and warm March, when temperatures of 23.6 degrees were recorded in Aboyne, Aberdeenshire, on March 27 - a new Scottish record for the month.
There was an average of 187 house of sunshine over England and Wales making it the sunniest March since 1929.
The only years to have a warmer March in the past 100 years were 1938, 1948, 1957, 1990 and 1997.
Paul Mott, senior forecaster at MeteoGroup, the weather division of the Press Association, said: "The weather in March has been quite exceptional. There were a number Scottish records that were broken and some of the highest temperatures ever recorded in March."
"It was really in the last 10 days of March that the weather became really warm.
"The warm weather is due to an area of high pressure that is sat over the UK and in late March the sun starts to get stronger, providing a lot of daytime heating."
Mott confirmed that the warm weather will not extend into April.
"It has certainly got colder with more unsettled weather on the way," he said.
He said it would be colder everywhere by today or tomorrow with rain and even some snow by tonight.
"In general this will just be over the hills in Scotland but also at a lower level. We are expecting 5-10 cm of snow in the hills and a light covering at a lower level in Scotland.
"I think we will be waiting quite a long time until we get another decent spell of warm weather like we have seen in the past 10 days."