Many accurate 1921 census transcriptions have already been added to the pub history site, including London, and parts of Middlesex. If you can contribute to the site, send me some details to Kevan, along with some description of the specific property.
Holborn index
There is also the Horseshoe and Magpie, in Bedford street which latterly becomes the Bedford Arms.
A listing of historical public houses, Taverns, Inns, Beer Houses and Hotels in Holborn - St Andrew, London.
Residents at this address
1829/H Donnison, Horse Shoe & Magpie, Middle row, Holborn/../../Pigots Directory
1833-34/Horatio Donnison, Horse Shoe & Magpie, 25 Middle row, Holborn/../../Pigots Directory
1836/James Pensam, Horse Shoe & Magpie, 25 Middle row, Holborn/../../Pigots Directory
1839/George Lyall, Horse Shoe & Magpie, 25 Middle row, Holborn/../../Pigots Directory
1841/G Lyall/../../../Post Office Directory
1841/George Lyall/Publican/50/Middlesex/Census
1841/Elizabeth Lyall/../40/Middlesex/Census
1841/Elizabeth Lyall/../17/Middlesex/Census
1841/Sarah Lyall/../16/Middlesex/Census
1841/George Lyall/../12/Middlesex/Census
1841/Henry Lyall/../10/Middlesex/Census
1841/Richard Smith/Male Servant/17/Middlesex/Census
1841/Margaret Ford/Female Servant/17/Ireland/Census
1842/George Lyall/../../../Robsons Directory
1843/George Lyall/../../../Kellys Directory
1848/Mrs Elizabeth Lyall/../../../Post Office Directory
1851/Mrs Elizabeth Lyall/../../../Kellys Directory
1851/Elizabeth Lyall/Victualler, Widow/50/St Andrews, Middlesex/Census
1851/Elizth Lyall/Daughter, Assistant/27/St Andrews, Middlesex/Census
1851/Sarah A Lyall/Daughter, Assistant/25/St Andrews, Middlesex/Census
1851/Fras J Lyall/Daughter, Assistant/23/St Andrews, Middlesex/Census
1851/Robt Lyall/Son, Clerk/18/St Andrews, Middlesex/Census
1851/Susan Marshall/General Servant/25/Nottingham/Census
1851/Geo Walker/Waiter/22/Bath/Census
1856/Mrs Elizabeth Lyall/../../../Post Office Directory
1861/Elizabeth Lyall/Licensed Victualler, Widow/61/City of London,
Middlesex/Census
1861/Fanny Julia Lyall/Daughter/33/St Andrew Holborn, Middlesex/Census
1861/Kate Servis/Servant/20/Clonnel, Ireland/Census
1862/Mrs Elizabeth Lyall/../../../Post Office Directory
September 1861/William Alfred Collingwood/Outgoing Licensee/../../Morning Post
September 1861/Edward Hodges/Incoming Licensee/../../Morning Post