Second weekend in December, so about the 10th.
Everyone else always seems to get their tree the first weekend in December though, and we have to take home a leftover wonky moulting orphan tree from B&Q and hide its blemishes with love and tinsel - actually last year's was so wonky that DH took it outside and performed Extreme Surgery on the rootball with a spade to get it to stand upright in the pot.