Large parts of Britain enjoyed sunshine and temperatures in double figures on the mildest day of the year so far.
However it may be only a taste of spring as cold air is due to come back to Britain next week.
Initial indications were that Tuesday's warmest spots were in the London area and Trawscoed near Aberystwyth in Wales where readings of 17C were made.
John Hutchinson, a forecaster with MeteoGroup, the weather division of the Press Association, said: "It turned quite sunny in a lot of places, with temperatures of 12 to 15 in many areas, rising to 17 in London.
"However, in parts of Nottinghamshire, Lincolnshire and East Yorkshire, there was thick freezing fog in the morning, and the fog lingered, meaning temperatures struggled to get much above 3C."
The mild temperatures are expected to remain for the rest of the week, particularly in the south, though there will be less sunshine and more cloud and rain.
Mr Hutchinson said: "Next week we can expect colder air to come back in for a time."
The mild weather came after a number of cold snaps hit Britain earlier this year, boosting sales of warm clothes and flu remedies.
Heavy snowstorms affected most of the UK in January causing severe disruption to schools and traffic and the deaths of at least nine people.
Persistent rain and a rapid thaw of snow and ice which followed went on to cause flooding in parts of the north and west of England.