I hadn’t thought of that, though it’s more about getting the result in time to travel? Getting a sample posted and tested over Xmas is not likely to be quick..
I have no idea of the logistics I'm afraid, but something to look into I guess... In the UK some of the private services have dedicated drop-off/collection points that hopefully avoid the seasonal post issues...
It doesn't need to be PCR. Lateral flow works as well. You should be able to get that done there in a pharmacy, or take one with you from the UK which you then register the result of online.
Can't you order in advance to take it with you?