The UK could be set for the warmest December in almost 70 years as temperatures of 16C, around 10C above the average for this time of year, left Britons sweltering.
The weather has been so mild that daffodils have been begun flowering as far north as Chester and Northern Ireland.
Temperatures in the London area are expected to reach 16C today - above the average for May in central England of 11.2C and far higher than the December average of 6C to 8C for the UK.
A band of tropical air coming off the Atlantic from the South West is behind the unseasonable weather, and temperatures are edging towards the all-time December high of 18.3C, set on December 2 in 1948 in Highland, Scotland.
Helen Rossington, a forecaster for MeteoGroup, said: "Yesterday we got up to 14C or 15C across the South West, but today just about everywhere is in double figures.
"In south east England, East Anglia and the London area highs are going to be around 16C. The average is around 9C at this time of year for that part of England."
The hottest December 16 in the UK was recorded in 1972 at Aber in Gwynedd, north west Wales, when it reached 17C, and Ms Rossington suggested records for December 17 and 18, at 17.8C and 18C respectively, could be under threat.
The warm weather has brought about some bizarre sights in gardens and parks across the UK, including daffodils blooming, despite their usual season for flowering being between February and May.
Wirral Bird Club posted on Twitter a photograph of daffodils flowering in Chester, saying: "The weather has gone mad. Daffodils in flower in mid-December in Chester," while another user showed a picture of daffodils in full bloom in Downpatrick, Northern Ireland.
Another Twitter user, under the name @diamondgeezer, posted a photograph of a field of daffodils in London's Olympic Park, saying simply: "#climatechange".
Not even the recent flooding in Cumbria could drown out the daffodils, with Kendal Gardening tweeting: "After floods have come the Daffodils! In the Lyth Valley in mid December! Madness!"
Ms Rossington said: "We have just had unsettled rain in Cumbria, but wind coming from the South and South West is drawing up tropical moisture and warmth as well, which means it is very mild air coming from that direction.
"Because we have had this strong jet across the Atlantic it has kept going for weeks and weeks."
Greg Dewhurst, a forecaster from the Met Office, said: "The weather pattern has brought low pressure after low pressure, with mild conditions from the South.
"We would normally expect a variation in the wind direction at this time of year, with wind from the North bringing high pressure and leading to overnight frosts and fog.
"But because it has been so mild, windy and cloudy it has not allowed for colder weather to settle in."
With such warm weather, a white Christmas seems a long way off at the moment - although forecasters warned it was too early for an accurate prediction.
Ms Rossington said: "At this stage I would say it is fairly unlikely. There is a chance that maybe Scotland might get some colder air, and a slight chance in the North they might get some snow, but in the South it is more likely to be unsettled.
"But it is very early days yet."
Bookmakers have shortened the odds on Christmas being the warmest in history in the light of recent forecasts.
Coral has slashed the odds from 5/1 to 2/1 on over the past 24 hours, and also believe the chance of a white Christmas is now a long shot.
Spokesman John Hill said: "We have pushed the odds out to evens from 1/2 in light of the recent forecasts, however, we will be sweating on Christmas Day because if there is now snow in the UK, we will be forced to pay out our biggest liability to date on a white Christmas."