New Year's Day temperatures have reached the warmest ever - with 16.5C recorded in St James's Park.
It comes after temperatures yesterday also marked the hottest New Year's Eve on record - with recordings of 16.5C in Bala, Wales, 15.8C and 15.4C measured in Merryfield, Somerset and Sutton Bonnington, Nottinghamshire.
Conditions were so warm in London that the popular Hampton Court Palace ice rink had to close when the surface began to melt, exactly 59 years after the nearby stretch of River Thames froze over during the Big Freeze of 1962.
By 11.30am on Saturday, 15.2C had been reached at Hawarden Airport in north Wales, just shy of the New Year's Day record temperature of 15.6C set in Bude, Cornwall, in 1916.
Met Office forecaster Dan Stroud urged people to "make the most of the warmth because a change is on the way as we go into the early part of next week".
Daytime temperatures are expected to plunge to as low as 3C in Edinburgh by Tuesday and 7C in London and Cardiff.
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The unusually mild weather is caused by low pressure over Ireland dragging warm air up from the coast of Africa.
It comes as forecasters have warned that 75mph winds will batter parts of the UK today - with strong winds and snow expected to cause chaos later this week.
A yellow warning was issued by the Met Office today covering the Highlands & Eilean Siar and Strathclyde in northern Scotland, where gusts of up to 75mph.
It is in place between 10am and 5pm today.
The Met Office warned that the storms could cause transport chaos, as well as possible power cuts.
The Met Office's digitised database contains figures going back to the 1850s. New Year's Eve in 2018 was mild too, as the mercury hit 14C in Dunrobin Castle Gardens in Sutherland, Scotland.
But the data also shows only three Decembers in 100 years have had less sunshine than this month.
Forecaster Craig Snell, of the Met Office, said: "One of the reasons we're getting the dull weather is the fact that it's been so mild. We're drawing in south-westerly wind from the Atlantic and it's also drawing in a lot of moisture.'
"It keeps us warm but also produces a lot of cloud. The globe is warming up so expect our winters to get milder.
"We always have milder spells throughout the year, so we can't link every mild spell to climate change, but we can say that extremes in our weather will become more common as we continue through this century."
It comes after what is likely to have been Britain's dullest December since 1956 with less than 27 hours of sunlight across the country on average.
