The University of Warwick Modern Records Centre hosts:
"an unrivalled collection of UK trade union, employers' and trade association archives. ... The Centre has produced an occupational guide to its sources, although family historians should note that many of the unions listed have not deposited membership records at the Centre."From blacksmith to woodworkers, 30 trades are covered. There are sometimes multiple unions for each trade. For example, 29 union archives for printing and paper workers.
Most of the information is not online. A few items are, such as "Obituaries from the Fortnightly Returns of the Operative Society of Masons, Quarrymen and Allied Trades of England and Wales." There is an index for 19,600 entries from 1836-1900 giving surname, first name, location, age at death, relationship to member, date of Fortnightly Return, date of death, cause of death and other information.
Thanks to Ken Mcleod for the info, via Glenn Wright