Overview of British Directories Online

Findmypast has just added 90 British directories and almanacs to a collection of volumes sourced from Anguline Research Archives, Gould Genealogy, Yorkshire Ancestors, Eneclann and Devon Family History Society. Dates range from the 1770s to the 1980s. Yorkshire is particularly well covered.
Each records consists of a transcript and an image of the original document that will reveal your ancestors address, occupation and business interests. Find a list of the complete collection of 226 volumes at www.findmypast.com/articles/britain-directories-and-almanacs-publication-list/.

The Genealogist (www.thegenealogist.co.uk) has 389 directories available to Diamond subscribers from 1677 to 1956. That includes 135 for London with the large Kelly Post Office directories for 1846, 1856, 1859, 1869, 1880, 1905, 1906, 1908, 1910, 1012, 1916, 1920-21, 1925-36, 1939-40.

Ancestry has a collection UK, City and County Directories, 1766 - 1946 with a more than 27 million item index created using text recognition software. There are 24 directories for London.

The University of Leicester Historical Directories collection http://specialcollections.le.ac.uk/cdm/landingpage/collection/p16445coll4 replaces the previous directories-online facility. It has directories from 1766 to 1919 with good coverage for London from the 1890 to 1910s and nearly 50 directories for Leicestershire. This is a free website.

If your interest is Scotland don't overlook the National Library of Scotland collection at https://archive.org/details/scottishdirectories