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.
Most sites on pub history (with about three pages of content) suggest that the pub started in Roman Times, as the Tabernae. It may be true, who cares?
In the London Morgans map of 1682 at the Layers of London site, there are many Inns listed, and it is just 16 years after the Great Fire of London in 1666. I list nearly 2,000 entries in 1682 in the Key to the Morgans map of London in 1682. the additional information being added to this key will help in perusing the map, plus there are links to many of the principal buildings, and pubs, Inns and taverns.
Or you could search over 60 thousand pages of pub history and London history by surname, street name or pub on my one site, the pubwiki, and also the londonwiki.
The londonwiki lists the entirety of the London 1832 street directory and also the 1842 street directory in images.
The pub wiki does record minute details of research of people, buildings and streets from diverse sources, including Pepys diaries and taverns visited, pub tokens, newspaper reports, masonic records of meetings, Sun Fire insurance records, early maps and street directories, and surveys of London, window and hearth taxes, licensing petty sessions records, census detail, births, christenings, marriages, deaths and wills. There are also a significant number of images of the buildings, business cards and other related material.
In addition to public houses, are the many coffee houses and taverns, Inns, chop houses and hotels. Many of these pre-date public houses, and many are now the exchanges for business, and were formerly a place for meeting associates, reading newspapers and share dealings. Here are the wine merchants, victuallers, coffee houses etc in 1809 from the London Holden directory. I am building the latest listing on the london taverns blog. Here are many thousands of London listings.