Adrian's 2000 year list numbering 383 is attached. It predates Lee splitting at least White Wagtail and Siberian Stonechat (I believe). I am not sure whether there is anything else?
There are 11 species first recorded in Ireland - Lesser Canada Goose, Gannet, Great White Egret, Short-billed Dowitcher, Whimbrel, Little Gull, Bonaparte's Gull, Ross's Gull, Gull-billed Tern, Pale-bellied Brent Goose and Blue-winged Warbler but I anticipate that Lesser Canada Goose, Short-billed Dowitcher, Bonaparte's Gull, Ross's Gull, Gull-billed Tern and (definitely!) Blue-winged Warbler are the only ones only seen in Ireland - so I anticipate a converted comparison to a British current UK400 Club list may be 379 for comparison (including White Wagtail and Siberian Stonechat)?
A conversion from there to a BOU British list would also deduct Ruddy Shelduck, Tundra Bean Goose, Greenland White-fronted Goose, Pale-bellied Brent Goose, Black Brant, Marbled Teal, Booted Eagle, Black-headed Wagtail, Desert Lesser Whitethroat and Siberian Chiffchaff so 369.
As the Ruddy Shelduck was on my patch, it should obviously have been accepted......
All the best