Snow has been confirmed in Braemar in Aberdeenshire, Shetland, Perthshire and the Scottish Borders. Footage from traffic cameras also reveals snow has fallen across the Yorkshire Dales in England.
A white Christmas is defined by the Met Office as when one snowflake is observed to fall in the 24 hours of Christmas anywhere in the UK.
A spokeswoman said: “There has been snow falling in the early hours of Christmas Day and we’re seeing some snow across Aberdeenshire, Perthshire and Shetland so it is officially a white Christmas.”
However, many parts of the country are more likely to see rain on Christmas Day although it will be cold and bright in northeast England and Scotland.
There are warnings of localised flooding in Northern Ireland where the rain is forecast to be especially heavy.
Snow is expected to be more widespread on Boxing Day with a yellow warning in place for parts of central and southern Scotland as well as northern England.
Half of recent Christmas Days have seen snowfall recorded somewhere in Britain, although widespread coverings dreamed of by are becoming rarer.
A widespread covering is when 40 percent of UK weather stations report snow on the ground at 9am. This has happened four times since 1960: in 1981, 1995, 2009 and 2010, according to the Met Office.
The last widespread white Christmas in the UK in 2010 was extremely unusual, according to the Met Office, as not only was there snow on the ground at 83 percent of stations – the highest amount ever recorded – but snow or sleet also fell at 19 percent of stations.
READ MORE ON BRITS ASKED TO GET BOOSTERS ON BOXING DAY
The Met Office warns of disruption to bus and train services with journey times probably taking longer.
Flooding affecting a few homes and businesses is also likely, according the the Met Office.
In southern Scotland and northern England there are warnings of snow and strong winds from midnight to midday on Boxing Day probably affecting higher ground and leading to possible disruption.
Some short term loss of power and other services is possible, the Met Office warns.
On Christmas Day, London was expected to see temperatures of about 7C dipping to 6C by noon. There is a chance of rain in the evening.
Manchester will be colder, dropping from 4C to 3C later in the day with a likelihood of rain after 10pm.
Edinburgh will see temperatures of 2C and 3C with no rain expected while Belfast is likely to see rain all day.
Forecasters say Cardiff will be about 8C or 9C on Christmas Day, but with rain expected throughout.