After long and frequent battles against prime minister Margaret Thatcher in the privacy of the cabinet, Francis Pym's final defeat came at a pre-election press conference in 1983.
Then foreign secretary, Lord Pym of Sandy, who has died aged 86, dared to contradict the prime minister in public. He said he would be satisfied with a majority of 50 to 100, while Thatcher proclaimed the sky as her limit.
Pym anticipated that, if Thatcher achieved her will, as indeed she did, his own days would be numbered - and they were.
Having previously been considered Thatcher's chief challenger, Pym was sacked as foreign secretary, the final role in which he and a long line of similar semi-patrician top Tories had failed to curb her more extreme policies.
Ironically, as defence secretary (1979-81), he had halved Thatcher's drive to cut defence expenditure by £500m, making less risky her 1982 gamble to retake the Falklands. As her foreign secretary (1982-83), he served her well by diminishing her isolation from the US and Europe.
The quiet way in which Francis Pym accepted relegation to the backbenches, and a successful return to the business world, was typical of this Old Etonian who, like fellow traditional Tory squires, found it difficult to slug it out with the Grantham grocer's daughter and her streetfighters. As Lord (Douglas) Hurd told Lord (Woodrow) Wyatt, Pym never thought it was the place of a woman to argue with a man.
Such was Pym's loyalty to the party he loved that he continued to hope that the former Tory voters who had deserted the party in 1997 could be persuaded to return. For many years after, he dragged himself into the Lords to vote as desired by the chief whip of a party largely reshaped in the Thatcherite mould.
To the end his advice was available, both officially and unofficially. He chaired the political honours scrutiny committee until 1999. More significantly, before the 1997 election, he was one of a handful of Tory peers who were willing to discuss a deal with Lord Richard, then Labour's leader in the Lords, for a group of 30-40 Tory hereditaries to survive in a Labour-reformed house.
The image of a courteous, sensible, socially conscious Tory traditionalist survives Pym. He was born in Penpergwn Lodge, Monmouthshire, into a rooted squirearchy.
John Pym, one of the MPs whose attempted impeachment by Charles I helped start the civil war, was a collateral ancestor. Francis was the fifth Pym to serve in the Commons over the course of 350 years. His father, Leslie Ruthven Pym, son of the Bishop of Bombay, was a landowner and land agent who became Conservative MP for Monmouth in 1939 and a whip.
Pym went to Eton, where he was a contemporary of Humphrey Lyttelton, but was not in his band. "We were in the school orchestra and I played the oboe. But the orchestra was a joke."
He went up to Magdalene College, Cambridge, but, in 1942, went into the 9th Lancers, serving in North Africa and Italy.
He was mentioned twice in dispatches and won the Military Cross for taking over the command of a tank company when a senior officer was wounded. He emerged a major. He was serving in north Italy when he learned that his father had died between being re-elected and the delayed count in the 1945 general election.
He returned to Cambridge to finish his degree and to take over the running of his families' estates. In 1947 he joined Lord Woolton's firm of Lewis's, the northern department store, and in 1948 was named the general manager of their subsidiary Merseyside Diaries.
In 1953 he used part of his inherited money to buy 11,070 preference shares and 500 ordinary shares in tentmakers George Holloway and Webb Ltd, becoming its managing director for the next eight years. He became a Lloyd's name in 1953.
Always interested in carrying on his family's parliamentary traditions, he became a member of Herefordshire county council (1958-61), and fought the hopeless beat of Rhondda West for the Tories in 1959.
Two years later the safe seat of Cambridgeshire became available when its sitting MP, Gerald Howard, became a high court judge. He remained an MP for Cambridgeshire until 1983, then for Cambridgeshire South East until 1987.
Francis emulated his father in climbing the whips' ladder, becoming an assistant whip in 1962, a whip in 1964, deputy chief whip in 1967 and chief whip in 1970, when Edward Heath became prime minister.
With the politeness of an Old Etonian and the reticence of the hereditary middle class, he only showed his emotions by the way his shoulders slumped.
Heath liberated him from the whips' office in 1973, to take over from William Whitelaw as Northern Ireland secretary. Because of Labour's unexpected victory in March 1974, this only lasted 12 weeks, just enough for him to conclude that Whitelaw's power-sharing Sunningdale agreement might just work, unusual for one of his pessimistic tendency.
In opposition, Heath made him spokesman on agriculture as well as Northern Ireland. Within weeks he had worked himself into a physical breakdown, and was forced to retire for three months to his farm in Sandy, Bedfordshire. Most observers thought he was through.
Significantly, he began his comeback campaigning for fellow patrician moderate Whitelaw against Margaret Thatcher in the 1975 leadership election.
In 1976, a victorious Thatcher named him shadow leader of the house, with additional responsibility for devolution. A moderate federalist, he sought to unite the Tories by arguing for a constitutional conference on the subject.
By 1977 commentators began to see Pym as possibly the next Tory leader because of his moderate reform proposal. When Thatcher named him shadow foreign secretary (1978-79) as well, his views seemed very Tory conformist. These included opposition to economic sanctions against apartheid South Africa.
When the Tories won the 1979 election, he was named defence secretary. Ordered by Mrs Thatcher to cut spending by £500m, he sided with the brass hats to cut that to £200m. He became so formidable an opponent that in 1981 she sacked Norman St John-Stevas as leader of the Commons to put Pym in that less dangerous position.
When Lord Carrington felt compelled to resign as foreign secretary for misjudging the Argentine aggression in the Falklands, Thatcher felt it necessary for Pym to replace him to shore up her endangered position.
He again urged caution, and encouraged the attempted American and Peruvian arbitration. But Thatcher preferred the gung-ho advice of Admiral Terence Lewin. When her high-risk strategy paid off, it guaranteed her victory at the 1983 election and his political demise.
Had she failed, he was her likely successor. He stood down at the election of 1987 and was created a life peer.
He is survived by his wife, Valerie, whom he married in 1949, and his four children, Charlotte, Jonathan, Andrew and Sarah.
· Francis Leslie Pym, politician, born February 13 1922; died March 7 2008