Sir Patrick Cormack has been an MP for almost 40 years
Long-serving Conservative MP Sir Patrick Cormack has announced that he will stand down at the next election.
The 70-year-old said the "unhappy events" following the MPs' expenses scandal had made the work of politicians "much more of a burden".
Sir Patrick, who represents South Staffordshire, failed in a bid to become Commons Speaker in June.
The MP, who has been in the Commons since 1970, said he was not retiring, merely "changing direction".
He is one of more than 100 MPs to announce that they will leave Parliament at the next general election, which has to be held by 3 June.
Sir Patrick 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."
Sir Patrick - the second longest-serving Tory MP after Sir Peter Tapsell - entered Parliament as MP for Cannock in 1970.
He transferred to South West Staffordshire, now known as South Staffordshire, 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, failing again in a second bid in June this year, after Michael Martin resigned over his handling of the MPs' expenses scandal.
In his statement, Sir Patrick 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."
Sir Patrick has been the chairman of the Northern Ireland select committee since 2005.
In 2007, factions in his constituency association tried unsuccessfully to deselect him as their candidate.
South Staffordshire is regarded as a safe Conservative seat, with Sir Patrick enjoying a majority of 8,847 at the last election.