The next edition (24th Edition) is due to be published on 31st March 2011. The pre-order price is £267. Details are available here.
Thomas Erskine May (later Lord Farnborough - though sadly this was the 2nd shortest peerage in British history - he died a week after his peerage was created) started work in the House of Commons aged 16 as an assistant librarian. After becoming a barrister he worked his way up as a parliamentary official until in 1861 he was appointed Clerk of the House of Commons. His "practical treatise" appeared in 1844.
In addition to his most famous work, he wrote a constitutional history (which can be downloaded as a free book here).