“EVERY time my father told a family story,” Conrad Russell once said, “I would ask him what happened next and he would say history does not relate. I was always sure it would relate if you asked it in the right way.” And history — the lessons of the past, and their bearing on the present — was the central preoccupation of Russell’s life, as a scholar, a politician and a campaigning, critical voice in public affairs.

The son of the philosopher Bertrand Russell, Conrad Sebastian Robert Russell was born in 1937. His father was reportedly so fond of the novelist Joseph Conrad that he named both his sons after him. The youngest son, Conrad spent much of his early childhood in America, where his father was teaching, and returned to England at 8. After a brief and unhappy spell at the progressive Dartington Hall School, he went to Eton and then to Merton College, Oxford.

The eccentric tone of his upbringing meant that he stuck out at school. Bertrand Russell was in his mid-sixties when Conrad was born, and he instilled in his son from an early age the principles of inquisitiveness and debate that he so cherished in his own work.

“As soon as I could form coherent sentences,” recalled Conrad, “I could argue with him and always take it for granted that I would be treated as an equal: my arguments would be treated with any respect they might deserve and, if I won, my victory would be conceded without fuss.”

His father taught him precision in language and the readiness to consider a case, as well as introducing him to many of the great thinkers of his own generation: at eight, for example, Conrad was discussing military strategy with Basil Liddell Hart over dinner. But, as he said of his childhood, “like James Bond, it reads better than it lives”. It was not until reaching Oxford that he found his feet among his peers. Once there, he attracted attention for his campaign with the late Paul Foot (obituary, July 20) to allow women to speak at the Oxford Union.

On graduating, he began teaching at Bedford College, London, where he would remain for almost twenty years, the last five of them as Reader in History. For five years from 1979 he taught at Yale University, then in 1984 he returned to London to take up a post at University College. In 1990 he became Professor of History at King’s College London, a position he held until his retirement in 2003.

Russell began research on the period leading up to the English Civil War in 1958, prompted by his mistrust of the prevailing wisdom about the conflict’s origins. It was a subject, he said later, that it took him 30 years to come to terms with. By the mid-1960s his research had convinced him that 17th-century members of parliament simply did not have the conceptual apparatus to be capable of having the ideas that most histories attributed to them, and that their incapacity to understand the cost of government had been a major factor in the movement towards war in 1642.

He found that each of the insights developed in his work opposed conventional portrayals of the civil war. In the main, such studies saw it as a smooth crescendo towards a struggle of high principle between parliamentary independence and monarchical tyranny. By contrast, Russell’s thesis was that England had almost fallen into war — through a clash between low taxation and increased public spending on war, through the English inability to comprehend the subsumption of English identity into an idea of “Britain”, and through the inability of government to enforce a single religious standpoint. “As they tell me in Westminster,” he wrote, “it’s not a conspiracy, it’s a cock-up”.

He worked on the subject for years, tackling aspects of it in works such as Parliaments and English Politics 1621-1629 (1979) and The British Problem and the English Civil War (1985) before publishing his main interpretative study, The Causes of the English Civil War, in 1990. Work followed on James VI; on divine rights in the 17th century; on judicial independence and on many other facets of the era.

Such views swiftly gained currency. and Russell came to be seen as a significant figure in the so-called revisionist school of British history. He did not share the conservative politics of other leading revisionists, but his work, like theirs, was notable for the challenges it posed to contemporary, as well as historical, ideas of Britain.

Russell’s historical research was conducted in parallel with his political career, which began in 1956 when he joined the Labour Party after the Suez crisis. He later publicly disagreed with his 93-year-old father’s decision to tear up his Labour Party membership card as a protest against the Vietnam War — “We do not see eye to eye on certain details,” he told journalists — and in 1968 he was scheduled to stand as the party’s prospective candidate for Mitcham and Beddington, but declined citing pressure of work. During the general election of 1974, however, he became convinced that the British electoral system had to be altered in favour of proportional representation. “Every time the Coal Board and the miners approached negotiation,” he later wrote, “the politicians recalled them to the class-based slogans which were essential to the unity of their parties . . . It is not until we change our electoral system that we can stop looking for scapegoats and start looking for solutions.”

Jeremy Thorpe’s political broadcast for the Liberals, concluding “If you agree with me, then vote for us,” clinched it. Russell joined the party.

He assumed the family title in 1987, on the death of his half-brother, and he became the Lib Dem spokesman on pensions and social security in the House of Lords in 1990. In the years that followed, his forensic brain, dry wit and historical knowledge distinguished him both as a potent advocate of the party’s principles and as one of its leading philosophers. His An Intelligent Person’s Guide to Liberalism appeared in 1999 to great acclaim.