'White Christmas' traditionally meant snow on the ground on the day. If we use that definition, instead of the ridiculous meteorological one, then I can remember nine white Christmases in or near Broxburn, West Lothian (80m asl) since 1962, which was the first I can recall. Here they are
1962: we woke up to three inches of snow that lay all day.
1967 or 68: we had a white Christmas one of those years, the snow falling the day before.
1970: there was a couple of inches of snow on the ground.
1981: we had a thin covering of snow and a sub-zero day.
1993: we had another thin covering that lasted all day.
1995: we had a couple of inches that had fallen the night of the 23rd and a sub-zero day.
2000: we had an inch of snow on the ground, a little falling and a sub-zero day.
2009: we had about eight inches of snow, which had been accumulating since the 17th. It was to keep building up for another fortnight.
2010: there was about three inches lying from a fall several days earlier. The thaw began that day.
That was Christmas days where there was at least a 50% covering. There were two Christmas days, 1980 and 1998, when it snowed and lay in the evening and a third day, 2008, when there were a few flakes of frozen snow on the ground. They may have been others, but from the white Christmases I can recall we have had between one white Christmas in five and one in seven in my lifetime, depending on your definition.