You can blame Dickens for the romantic myth of a snowy Yuletide. Bing Crosby may have been dreaming of a white Christmas, but we may as well forget it - if the statistics are anything to go by.

Snowmen and skiers, romantics and punters all dream of a white Christmas and generations of children have grown up to expect snow on Christmas morning. Decorations, carols and cards all bear witness to its perennial presence: the tradition of snow is deeply seated in English culture, but how often does the annual dream reflect the reality?

This century, there have been just four truly white Christmases in the southeast - occasions when the 25th has brought the smooth tranquility of a fresh fall of snow. That of 1906 was unremarkable; 1927 brought skiers to the Chilterns and Dunstable Downs, and 1938 had snow on every one of the 12 Days of Christmas. A deafening clap of thunder just before midnight on Christmas Eve in 1970 heralded London's last true white Christmas. Bookmakers for once might be considered generous in designating 1976 white, if only on the criterion that at least one fleck of sleet fell on the London Weather Centre's roof on the 25th. Similarly, speckled Noels were recorded in 1956, 1964, 1968 and 1996 - all, oddly enough, leap years, just like 1976. The great freeze of 1962-3 does not figure in either of these lists. The coldest winter since 1740 froze the Thames at Kingston in January and produced mountains of snow, but not until Boxing Day. Similarly, 1981, when the coldest December on record produced sea ice off the East Anglian coast, failed to give snow on Christmas Day.

With just nine white Christmases this century, the tradition of Christmas snow is clearly a myth, whose origins appear to lie in "The Little Ice Age" which had us in its grip between 1550 and 1850. It was a period of much cooler climates that at present, and was famous for the severity of its winters. In "The Great Winter" of 1607-8, trees died of frost and ships were stranded miles out into a frozen North Sea. "Frost Fairs" were regularly held on the Thames throughout the 17th and 18th centuries, and white Christmases were commonplace - all the more so because, until 1752, the Julian Calendar put Christmas Day four days into January, always a cooler and more snowy month. The Thames last froze in 1814, but even into Dickensian times, England's winters were appreciably more harsh than they are today. The spectacular white Christmas of 1835 was immortalised in the Pickwick Papers, and the scenes Dickens describes - perhaps typical of the time - undoubtedly provided the inspiration for today's association of Christmas with snow. The same White Christmas of 1836, however, had tragic consequences for the people of Lewes, East Sussex, where an avalanche demolished two houses and caused eight deaths. To this day, the disaster is commemorated in the name of a local pub, the Snowdrop.

The concluding part of this review of White Christmases will appear tomorrow.

Stephen Roberts is the founder and Director of Weathernet, a company dedicated to the collection of detailed weather information, particularly in connection with insurance claims validation.

Weathernet is part of the Cunningham Group.