Staffordshire MP Sir Patrick Cormack, one of the longest-serving and most respected Members in the Commons, has announced that he will not be fighting the next general election.
Sir Patrick, 70, said in a statement that the “unhappy events” of recent months had made working hours at Westminster much more of a burden than before.
He said: “It is also becoming increasingly clear that the new House of Commons will be very different from the old.
“Sadly, I have come to the conclusion that it is right that I should hand the torch to a younger man or woman.”
He said this was “the most difficult decision” of his life, but insisted: “I am not retiring - I am merely changing direction.”
The news will come as a blow to Tory leader David Cameron, as Sir Patrick - the second longest-serving Tory MP after Sir Peter Tapsell - has a wealth of parliamentary experience behind him and probably knows more about the House of Commons, its ways and its history, than any other Member.
Sir Patrick, who has been described as a politician, historian, journalist and author, entered Parliament as MP for Cannock in 1970, ousting Jennie Lee, widow of Aneurin Bevan, founder of the National Health Service.
He transferred to South West Staffs (now known as South Staffs) in February 1974, a seat he has represented ever since.
Sir Patrick was knighted in 1995 for services to Parliament, and in 1997, after 27 years as a backbencher, he was promoted to shadow deputy leader of the Commons. He resigned in 2000 to run for the Speakership but was unsuccessful, as he was again in a second bid for the Speakership earlier this year.
Since 2005, he has been the chairman of the Northern Ireland Select Committee.
In 2007, an unsuccessful attempt was made by factions in his local constituency party to deselect him as their candidate.
He has an unrivalled knowledge of the history of Parliament, British castles and English cathedrals, and has written books on these subjects.
In his statement he said: “I have informed the Leader of the Opposition, the Speaker, and the chairman of South Staffordshire Conservative Association that, after a great deal of careful thought, and family discussions, I have most reluctantly decided not to offer myself for re-election at the next general election.
“I have been immensely proud to have been a Staffordshire Member in the world’s greatest Parliament for close on 40 years, much more than half my life.
“I regard membership of the House of Commons as the highest honour to which any British subject can aspire and I shall always be grateful to have had the opportunity, and the great privilege, of serving my country and my constituency at Westminster.
“I am most anxious to continue to work for some of the causes I have campaigned for over the years but I have recently had my third severe attack of bronchitis in two years and my doctor tells me I really ought to cut down on my normal ‘term time’ working week of 70 to 80 hours.
“The unhappy events of recent months in Parliament have made those hours much more of a burden than they used to be and it is also becoming increasingly clear that the new House of Commons will be very different from the old.
“Sadly, I have come to the conclusion that it is right that I should hand the torch to a younger man or woman, someone who will, as I have done, be able to offer many years of service to the people of South Staffordshire.”
Tory leader David Cameron said: “I am extremely grateful to Sir Patrick Cormack for his long-standing and committed service to his constituency and to our Parliament.
“As chairman of the Northern Ireland Select Committee, as warden of St Margaret’s, Westminster, and as a leading backbencher, Sir Patrick has been an outstanding servant of our Parliamentary democracy.
“At the next election, we will be losing a great friend to the party and to our Parliament.”