<P> In the United Kingdom, white Christmases were more common from the 1550s to the 1850s, during the Little Ice Age; the last frost fair on the River Thames, however, was in the winter of 1813--14 . The shift from the Julian to the Gregorian calendar in 1752 also slightly reduced the chance of a white Christmas, effectively moving Christmas earlier in the winter . An "official" white Christmas is defined by the Met Office as "one snowflake to be observed falling in the 24 hours of 25 December somewhere in the UK", but formerly the snow had to be observed at the Met Office building in London . By the newer measure, over half of all years have white Christmases, with snow being observed 38 times in the 54 years to 2015 . A more "traditional" idea of snow - covered ground is less common, however, with only 4 occasions in the 51 years to 2015 reporting snow on the ground at 9am at more than 40% of weather stations . </P> <P> Although most places in the UK do tend to see some snow in the winter, it generally falls in January and February . However white Christmases do occur, on average every 6 years . </P> <P> Christmas 2009 was a white Christmas in some parts of Britain, with thick lying snow which easterly winds had brought over the previous week . Travel over much of Britain was badly affected by ice and snow on roads, and was made more slippery by partial daytime thaw followed by overnight refreezing . It was the first white Christmas anywhere in the United Kingdom since 2004 . </P> <P> In Ireland, the prospect of early winter snow is always remote due to the country's mild and wet climate (snowfall is most common in January and February). Bookmakers offer odds every year for a white Christmas, which is officially lying snow being recorded at 09: 00 local time on Christmas Day, and recorded at either Dublin Airport or Cork Airport (bets are offered for each airport). Since 1961, countrywide, snow has fallen on 17 Christmas Days (1961, 1962, 1964, 1966, 1970, 1980, 1984, 1990, 1993, 1995, 1998, 1999, 2000, 2001, 2004, 2009 and 2010), with nine of these having snow lying on the ground at 09: 00 (1964, 1970, 1980, 1993, 1995, 1999, 2004, 2009 and 2010). The maximum amount of lying snow ever recorded on Christmas Day was 27 cm (11 in) at Casement Aerodrome in 2010 . </P>

When did the uk last have a white christmas