Since you are looking for a White Christmas, let me suggest that you consider elevation as well as latitude. North is good, and High is better. Here in Pennsylvania, USA, one is much more likely to find snow in the mountains than closer to sea level.

I hope you find your White Christmas. Have you considered leaving the UK in search of snow?

Also, we will be in London in early September. Any possibility of a GTG?

Hope this helps, Debbie in Pittsburgh (but only for 8 days)