Forecasters are also warning there will be more heavy rain to come for parts of the waterlogged North West already devastated by flooding from storm Desmond. Over two inches are expected for Lancashire and Cumbria from tonight as an Atlantic front moves in.
Yesterday parts of the UK basked in temperatures as high as 17C (62.6F) in the South while the North are experiencing 8c to 9c (46.4 to 48.2F).
And the “exceptionally warm” weather is set to continue with Scotland seeing temperatures as high as 13C (55.4F)
The average maximum temperature for the UK in December is 6.7C (44.06F).
Lindsay Mears from the Met Office said: “It is pretty mild for this time of year, which is quite exceptional.
“It’s due to the warm air forming in from the Atlantic and bring with it a lot of rain and cloud, which keeps the temperatures quite mild, instead of the bright clear skies which we see when temperatures go down.”
And the accompanying cloud and showers and persistent rain, which will carry on throughout the rest of the week.
“On Wednesday Scotland will be getting a bit warmer up to 12C to 13C.
“The temperatures for the whole country are quite amazing for this time of year.
“Things will be getting very windy on the south west, and the area will be battered by severe gales and that will move though quickly, and it will ease off.
“Up to Thursday things will continue to be pretty mild and the same, but unfortunately we have another warning out for the North West for heavy rain.
“This is a yellow warning, as the rain will be falling on already saturated ground, which is not good news.
“It will be about 20-40mm (0.8 to 1.5in), 50-60mm (1.9 to 2.3in) at the most exposed sites, falling on saturated ground which will not help the situation there and people need to be aware there will be more rain on the way.
“The rain will start just after midnight on Thursday and that will continue until 6pm.
“The area of rain is expected to move north eastwards into northern England clearing in the afternoon, but there will be heavy showers over Lancashire and parts of Cumbria.”
On its website, the Met Office said “there is a very low likelihood this may lead to renewed disruption from flooding in some recently affected areas.
“This would usually not be of concern but following recent severe flooding, these areas are more responsive to relatively small amounts of rain.”
Forecasters say moving into Friday the wind direction is set to change and come from the west bringing fresher air.
However Lindsay Mears said: “It’s only relatively fresher as the temperatures have been so high, and they will be going down to 12C and 13C, which is still well above average for the time of year.”
It looks as though mild unseasonable weather is set to continue into the festive week bringing doubts about a while Christmas.
Ms Mears said: “We are looking at a bit of an unsettled picture, so carrying on with the rain and cloudy in areas, but it’s too early yet to say what will happen yet.”
Explaining the mild spell, she said: “The weather hasn’t changed particularly, it’s just to do with where the wind coming from, and at the moment it’s coming from the Atlantic.
“Sometimes we might the continental cold air, or the Scandinavian air.
“It’s not unusual to have storms, rain, wind and cloudy weather at this time of year, but the temperatures are a lot warmer than average and are exceptionally warm for this time of year.
“But it is still very early in the winter and we are only just getting the season.”
The last time temperatures were this high was in 1994 when the mercury climbed to 17.7C (63.86) in Penkridge, Staffordshire.
Britain could be heading towards the warmest December since 1948, which saw a record high of 18.3C (64.94F) in the Highlands.