The forecaster said December 25 will be damp and windy but especially mild, with highs of 13C or 14C.
The hottest Christmas Day on record was 15.6C in 1920, so there is a “small chance” of it being a record, the Met Office added.
Meteorologist Liam Eslick said there may be snow on Christmas Day on mountains in Scotland, but it is “not looking likely that there will be a white Christmas in England”.
He added: “It’s looking like a damp picture across the UK, heavy rain possibly in Wales, past Christmas lunch there could be some breaks if people are looking to go out and about.
“Boxing Day is probably going to be the best day if people are looking to go for a walk.”
He added that Christmas Day is expected to be a lot milder than usual, with the average December temperature between 7C and 8C, but the top temperature that could be seen this December 25 is 14C.
Mr Eslick said there is a “small chance” the UK could see the warmest Christmas Day on record.
Meanwhile Christmas Eve travel plans could be ruined with heavy winds set to batter parts of the country.
Gusts as high as 70mph are due to hit the north of Scotland and northern and central areas of England.
Two separate yellow wind warnings have been issued, saying people should expect travel disruption, damage to buildings and power cuts, while the rest of the country may see showers.
Mr Eslick said: “People should make sure to leave more time, especially in exposed areas, it could affect rail networks and ferries.
“People travelling on roads should take care and stay away from high-sided vehicles and, for people who are at home and are going for walks, stay away from coasts.”
A yellow warning for rain is in force covering much of Wales, with forecasters warning that flooding and travel disruption is possible, and will last until 6pm on Christmas Eve.
Between 20mm to 40mm of rain is expected widely and 60mm to 80mm on higher ground.
Another yellow rain warning is in force for western Scotland until 11.45pm on Saturday, with 20mm to 55mm of rain expected widely and 80mm to 100mm on higher ground.
A snow and ice warning is in place for north and east Scotland until 3pm on Saturday.
