There is disappointing news for anyone hoping for a white Christmas — the latest computer-generated weather forecasts point to a Christmas Day without snow.

After the coldest start to December for more than 30 years, and with snowfall seen in many parts of Britain as early as October, the bookmakers could reap the dividends after taking a record number of bets on a white Christmas.Because of the cold snap, the odds for snow falling on Christmas Day in London were reduced to 4/1. A British white Christmas, though, is a rare event, having occurred only ten times since 1900.

A sustained dry spell is forecast over the next week because of high pressure. A strong high-pressure system blocks depressions, forcing the accompanying wet and windy weather to make a “detour”, so there could be clear skies over much of Britain on Christmas Day. Temperatures will depend on where the centre of the anti-cyclone is anchored — indications are that it might drift northwards and sweep in cold, dry air from Europe.

With clear skies, it is possible that frost and fog may follow a freezing Christmas Eve night and, first thing in the morning on December 25, it could almost resemble snowfall.

But all is not lost. The bookmakers’ definition of a white Christmas is for a single snowflake to fall anytime within the 24-hour Christmas Day period at a specific location. This year, in London, it will be Buckingham Palace.

In rare circumstances, snow can fall from a clear blue sky. This is most likely to happen in the Arctic or Antarctic, where moisture in the air is frozen into fine crystals of ice that resemble tiny diamonds, or snowflakes, known as “diamond dust”. The phenomenon occurred this February during bitterly cold weather in various parts of England.

For those interested in more outlandish weather phenomena, William Hill is offering odds of 100/1 for the River Thames to freeze over between Westminster Bridge and Tower Bridge in London, although this has not happened since 1814.

In the future, it seems that a white Christmas will become even more of a dream. According to climate predictions, the chances of snowfall at Christmas in Britain will drop by up to 65 per cent by 2050, as the winters become milder.