The previous record of 14.8C had already been broken at 11am when the mercury hit 14.9C in Ryehill, East Yorkshire, and then again at noon when temperatures in Coningsby, Lincolnshire reached 15.3C.
The record-breaking temperatures on New Year’s Eve followed what was described as a “much milder” December than usual.
Met Office forecaster Craig Snell told the PA news agency: “December itself has been warmer and we have seen temperatures of up to 18C in parts of the UK.
“In the grand scheme of things, it was above average but not as high as it could have been but this New Year’s Eve is the warmest we have had.
“The interesting thing is that it is usually localised but this year, anywhere south of Glasgow or Edinburgh has been really mild and there have been plenty of places reaching 14C or 15C.”
Mr Snell said the rise in temperatures has been put down to “south-westerly winds” that “brings milder weather to our shores”.
He added: “Where it’s coming from is warm enough it has allowed us to break records.”
It's been a very mild day with the warmest #NewYearsEve on record for the UK, England & Northern Ireland.
Both Merryfield & Nantwich recorded 15.8 °C, with Murlough recording 14.3 °C
Although Wales & Scotland didn't see their warmest on record it was still a very mild day here pic.twitter.com/3vyFF9z47R
— Met Office (@metoffice) December 31, 2021
New Year’s Day is expected to be almost as warm.
Mr Snell said the record for the warmest New Year’s Day stands at 15.6C, but this year it is expected temperatures will reach 14C or 15C.
“It’s not out of the realms of possibility,” Mr Snell said.
“It is the first time since December 2016 that we have had three consecutive days reach 15C. It has been a prolonged mild spell.
“It may break records tomorrow, but I was much more confident we would see record-breaking temperatures on New Year’s Eve because the record for New Year’s Day is a bit higher.
“It will still be an exceptionally mild start to 2022. The UK’s average is around 7C or 8C, so even at 14C it is still a good 7C above where it should be.”
Mr Snell said it is expected there will be a drop in temperatures in January, following what is likely to have been Britain’s dullest December since 1956, with less than 27 hours of sunlight 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.