The UK400 Club List of British and Irish birds has the following differences from the BOU list

The UK400 Club does NOT recognise Feral Pigeon nor Scottish Parrot Crossbill, the latter considered an isolated form of Parrot Crossbill. Slender-billed Curlew is also not accepted (the most recent claim is considered to relate to Eurasian Curlew).

Pacific Diver (considered distinct from Black Throated Diver)
Masked Booby (1-2 records)
Atlantic Yellow-nosed Albatross (2 records of one individual)
European White Pelican (several records)
American Least Bittern (1 record)
Chinese Pond Heron (Category D)
Sacred Ibis (Category C vagrant from population in France)
Greater Flamingo (several records considered genuine vagrants)
Chilean Flamingo (Category C vagrant from feral population in Germany)
North American Whistling Swan (considered distinct from Bewick’s Swan)
Ross’s Snow Goose (numerous records, vagrants from North America where species has undergone 71% increase in population; record 4 birds in 2007/8 winter)
Greenland White-fronted Goose (considered distinct from Eurasian/Pacific)
Tundra Bean Goose (considered distinct from Taiga Bean Goose)
Pale-bellied Brent Goose and Black Brant (both considered specifically distinct from Dark-bellied Brent Goose)
Ruddy Shelduck (mix of vagrants and Category C vagrants from Russia and elsewhere)
Bar-headed Goose (Category C vagrant from feral populations in The Netherlands)
North American Wood Duck (1 record - vagrant male in North Sea)
Falcated Duck (numerous records - Category D)
Marbled Duck (numerous records, clear pattern of vagrancy)
Baikal Teal (several records, one at least on Category A)
Cinnamon Teal (1 record considered vagrant - Outer Hebrides)
White-winged Scoter (1 record - NW Scotland)
Hooded Merganser (numerous records, clear pattern of occurrence)
White-headed Duck (numerous records including influx years; clear pattern of occurrence)
Eurasian Black Vulture (1 record - considered Vagrant)
North American Bald Eagle (1+ records)
Booted Eagle (at least 4 records - considered vagrant)
North American Hen Harrier (considered distinct from Hen Harrier)
Red-shouldered Hawk (1 ship-assisted vagrant)
Saker (records under consideration for recategoristaion - currently in Category E)
Lady Amherst’s Pheasant (Category C - 7 males still survive)
Hudsonian Whimbrel (considered distinct from Eurasian Whimbrel)
Caspian Gull (considered distinct from Herring Gull)
Thayer’s Gull (5 accepted records from Ireland; at least 4 others under review)
North American Least Tern (1 record; considered distinct from Little Tern)
Elegant Tern (at least 5 records)
North American Black Tern (6+ records mainly from Ireland; considered specifically distinct from Black Tern)
Eurasian Eagle Owl (population of 44 pairs in UK of unknown provenance; accepted to Category D)
White-rumped Swift (single record from Ireland)
Monk Parakeet (status being reviewed, feral population currently just under 100 individuals)
Middle-spotted Woodpecker (1 record, East Kent)
Northern Flicker (ship-assisted vagrant to Ireland)
White Wagtail (considered distinct from Pied Wagtail)
Amur Wagtail (considered distinct from Pied Wagtail; 3 vagrant records)
Black-headed Wagtail (numerous records; considered distinct from Yellow Wagtail)
Eastern Yellow Wagtail (10+ records; considered distinct from Yellow Wagtail)
Eastern Common Nightingale (3 records; taxonomic status currently under review)
Siberian and Caspian Stonechats (both vagrants and both considered specifically distinct from Common Stonechat)
Bicknell’s Thrush (vagrant on Scilly 1 record; considered distinct from Grey-cheeked Thrush)
Red-throated Thrush (1 record in Essex; considered distinct from Black-throated Thrush)
Naumann’s Thrush (3 records; considered distinct from Dusky Thrush)
Desert Lesser Whitethroat (10+ records; considered distinct from Lesser/Siberian Lesser Whitethroats)
Eastern Subalpine Warbler (regular vagrant; considered distinct from Western/Moltoni’s Subalpine Warblers)
Sykes’s Booted Warbler (8+ records; considered distinct from Booted Warbler)
Siberian Chiffchaff (considered distinct from Common/Scandinavian Chiffchaffs)
Two-barred Greenish and Green Warbler (both vagrants and both considered specifically distinct from Greenish Warblers)
Asiatic Brown Flycatcher (2 vagrant records)
Mugimaki Flycatcher (1 record - considered vagrant)
House Crow (ship-assisted records to Ireland)
Daurian Starling (2 vagrant records)
Mealy, Greenland and Scandinavian Arctic Redpolls (5 species recognised by UK400 Club but may all relate to one North-south cline of single species)
Pine Siskin (ship-assisted record)
Field Sparrow (ship-assisted record)
American Goldfinch (ship-assisted record in Ireland - still under review)
Rusty Blackbird, Yellow-headed Blackbird (several records)
Brown Thrasher (ship-assisted record)
Spotted Towhee (ship-assisted record)
Red-headed Bunting (numerous records; clear pattern of summer vagrancy)