The IOC Western Palearctic list uses a subset of species from the complete world taxonomy maintained by the IOC and which is updated regularly at www.worldbirdnames.org. As from 1 January 2018, this is exactly the same taxonomy used for the official BOU British List.
The geographical limits of the Western Palearctic are as defined by the nine-volume Birds of the Western Palearctic - basically Europe, North Africa and a block of the Middle East roughly south and east to Kuwait, but not including Iran nor anywhere east of the Urals and Caspian Sea. For more precise definitions, see BWP.
This is the most up to date Western Palearctic list, and is the recommended one to use for Western Palearctic lists on BUBO Listing.