Royal Mail's page about the last posting dates is not the most obvious name nor was it too easy to find on their website. I had to look up international mail and then enter 'Christmas' in their help centre search but I found it eventually. I have an idea they might move that page before the final Christmas rush so I have also included a link to their downloadable .pdf guide as well.
The last thing any seller wants is for you to be disappointed by parcels not arriving in time. On most of the sites we use, where we have that facility, we will warn you about the time it can take for International Economy (surface mail) to reach you. In many cases you may find that International Standard (airmail) is only a little more expensive and that by using it early you can be assured of delivery in good time.
The last posting dates from UK by International Economy (surface mail) to everywhere except Eastern and Western Europe are now in the past and I wouldn't suggest using that service at all when International Standard (airmail) to that region is only fractionally more.
The last recommended posting dates from UK by International Standard (airmail) are:
3 December - Asia, Far East (including Japan), New Zealand
4 December - Australia
5 December - Africa, Caribbean, Central & Sth America, Middle East
8 December - Cyprus, Eastern Europe, Greece
9 December - Canada, Poland
12 December - USA
13 December - Western Europe (excluding Greece, Poland)
