I have found the following books very useful:

Bennett, Douglas - Collecting Irish Silver,  Souvenir Press, 1984

Crisp-Jones, Kenneth, ed. - Silversmiths of Birmingham and Their Marks, 1750-1980,  Robert Hale, 1981

Culme, John - Directory of Gold and Silversmiths, Jewellers and Allied Traders 1838-1914,  Antique Collectors' Club, 1987

Fallon, John - Marks of London Goldsmiths and Silversmiths c1697-1837,  David & Charles, 1972

Fallon, John - Marks of London Goldsmiths and Silversmiths 1837-1914,  Barrie & Jenkins, 1992

Gill, Margaret A.V. - A Handbook of Newcastle Silver,  Frank Graham, 1978

Grimwade, Arthur - London Goldsmiths, 1697-1837: Their Marks and Lives,  Faber & Faber, 1990

Harrison, Miles - Exeter & West Country Silver 1700-1900,  Berforts Group, 2014

Pickford, Ian, ed. - Jackson's Hallmarks, pocket edition,  Antique Collectors' Club, 1991

Pickford, Ian, ed. - Jackson's Silver and Gold Marks of England, Scotland and Ireland,  Antique Collectors' Club, 1997

Priestley, Philip T. - British Watch Case Makers 1670 to 1970,  NAWCC, 2018

Ridgway, Maurice H. & Priestley, Philip T. - The Compendium of Chester Gold & Silver Marks 1570 to 1962,  Antique Collectors' Club, 2004

Turner, Richard W. - Illustrated Directory of Scottish Provincial Silversmiths & Their Marks,  Discus Publishing, 2014

Watson, B.W. - The Sheffield Assay Office Register,  Wm Townsend & Sons, Sheffield, 1911

Wyler, Seymour B. - The Book of Old Silver, English, American, Foreign,  Crown Publishers, 1937
    [Note: The attributions in this book should be treated with caution as there are a number of errors, probably copied from earlier editions of Jackson]