The Nexus 6 is back in stock on the UK Play Store, but you probably won't get it in time for the holidays. The listing mentions that the device will leave Google's warehouses in three to four weeks.
Google is currently selling the 32 GB variant in blue, with the silver version and 64 GB model still not available from the Play Store. The 32 GB model will set you back £499 ($790).
Retailers like Clove are taking pre-orders for the next batch of devices, with stock set to arrive in late December. O2 has also mentioned that fresh stock will be arriving shortly, as has Unlocked-Mobiles.
If you're intent on getting your hands on the Nexus 6 right away, Carphone Warehouse is selling the 32 GB variant (in blue) with free next day delivery.