New Year's Eve is already the UK's warmest since records began - with temperatures anticipated to exceed those expected in both Nice and Rome today.
Forecasters for the Met Office say conditions are "ridiculously warm" for the time of year as the average daytime high for December is just 7.6C (45.7F) in England and Wales.
But temperatures are expected to remain as mild as 17.2C in some parts today, smashing 2011's December 31 record of 14.8C set in Colwyn Bay in north Wales in 2011.
Recordings of 15.8C and 15.4C have already been measured in Merryfield, Somerset and Sutton Bonnington, Nottinghamshire, respectively.
Temperatures are expected to be 16C today in Nice and Rome while those in Cyprus will only enjoy 15C.
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.
An area of low pressure over Ireland is dragging warm air up from the coast of Africa.
So tomorrow could also be around the New Year's Day record of 15.6C (60F), set in 1916 in Cornwall. The December record for England is 17.7C (63.9F) in 1985, while for the UK as a whole it was 18.7C (65.7F) in 2019 in Scotland.
Rachel Ayers, meteorologist for Met Office, said: "In the south of the UK the weather should be dry so people should be able to enjoy dry weather with some bright spells around.
"For New Year's Day, another band of rain is pushing in from the west so the further east you are the drier your day will be with some bright spells."
She said there is a a "good chance" New Year's Eve will be the mildest ever, according to Mail Online.
Areas of southern and eastern England including the West Country, London and Lincolnshire, are expected to see the mildest weather.
Stephen Dixon, also of the meteorologist, said: "Our station at Ryehill, a small village in East Yorkshire has recorded 14.9 degrees today, which tops the previous record of 14.8. It has provisionally broken the New Year's Eve record.
"We would expect that to climb further and reach temperatures we saw yesterday of around 15.5 degrees."
Across Northern Ireland, Scotland and northern England, cloud and outbreaks of rain will linger for much if not all of the day, though it will become patchier.
But it will be a windy day for many, particularly across north Wales and northern England.
Yesterday, surfers made the most of the waves in Bournemouth, Dorset, while in London jugglers in their shirtsleeves performed on unicycles in Covent Garden.
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.
The dull weather is as a result of the mild temperatures, forecasters said.
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.
The Met Office said there had been just 26.6 hours of sunshine over 30 days - 38% less than the national average for this time of year.
The figure places this month in the running to become one of the 10 dreariest Decembers on record, forecasters said.
Britain's dullest December was in 1956, when 19.5 hours of sunlight was the national average, while the brightest was in 2001 with 64 hours recorded on average across the UK.
