Today is the warmest New Year's Day on record, with a temperature of 16.2C (61.1F) recorded in St James's Park, London - but more typical January weather is expected from next week when Arctic air could bring frost and snow to some parts.
Today's provisional figure easily beats the previous record of 15.6C (60F), with the UK continuing to experience "exceptionally mild" weather for the time of year.
Friday saw temperatures reach 15.8C in Merryfield, Somerset, and Nantwich, Cheshire, which beat the previous New Year's Eve record of 14.8C.
The Met Office later announced that temperatures rose overnight in some parts of the UK, with Bala in Wales reaching 16.5C to make New Year's Eve provisionally the warmest on record.
Although the higher temperature was reached overnight, the Met Office uses the 9am-9am time period for historical records.
Met Office meteorologist Dan Stroud told Sky News: "The warmth that we've had today and over the last few days is really thanks to a deep southwesterly wind.
"The air that we've got with us at the moment originates from the Azores, which is quite a warm source, so that's been drawn up right across the UK for the last few days.
"It's not expected that we get the weather from that direction."
Mr Stroud urged people to make the most of the current conditions, with the weather set to turn wintry next week with cold winds originating from the Arctic.
Parts of the North can expect widespread frost overnight with the possibility of snow in parts of Scotland.
Daytime temperatures are expected to plunge to as low as 3C in Edinburgh by Tuesday and 7C in London and Cardiff.
The Met Office issued a yellow weather warning for wind and snow across northern parts of Scotland between midnight on Tuesday to 6am on Wednesday.
Strong winds and frequent snow showers were predicted to cause travel disruption.
Mr Stroud said: "We are going to be losing the sub-tropical air flow and replacing it with some things from the north.
"Temperatures will definitely go back to average, with a return of frost and some snow in the forecast across north areas and across the hills."
The average temperature in December and the beginning of January is usually around 7C or 8C.
The balmier-than-usual start to the year saw people happily take part in traditional New Year's Day swims across the country, including at Derby Pool, New Brighton, Wirral.
One victim of the warm weather has been the ice rink at Somerset House in London, which was closed today.
A Twitter account for Somerset House said the "difficult decision" was taken "due to the effect of the ongoing warm temperatures on the quality of the ice".
Customers will be given a full refund.