as said, nhl.com will do them although i dont use them as their shipping rates to England are (or were, last time i checked) extortionate.
Alternatively, try
http://www.icejerseys.com . If you are after an authentic jersey it likely wont arrive in time for christmas as apparently there are some major holdups with the authentics due to problems at CCM/reeboks end, but replica jerseys should not be affected.
If you are after something a bit different, you should be able to get an Ovechkin: Dynamo Moscow russian jersey from
russianjerseys.com . I also know of someone who has some sort of business relationship with Lutch (makers of russian jerseys) and can get pretty much any russian jersey you want (if made by lutch) - let me know if you want their details.
Hope that helps