Few involved in British politics doubt that Robin Cook is a man of brilliant ability.

His waspish analytical skills came to the fore when he delivered a bravura Commons performance responding to the publication of the Scott report into the Tory arms to Iraq affair.

Quick witted and articulate he was the model prosecutor.

But with his brilliance comes a character many consider to be deeply flawed.

As foreign secretary he argued the case for conflict in Kosovo - but could not stomach the case for a war in Iraq.

Despite his principled stand a colleague and old enemy said he is walking from government as a loner.

"There will be little or no collateral damage," he said. "He was hardly someone who kept people on side. He was looking for a reason to go."

Cook's sharp political brain and brilliant debating skills were coupled with a failure to build alliances with colleagues who thought he was too clever by half.

Interviewed on Desert Island Discs, the Livingston MP conceded that he had, in the past, often acted without due consideration for others.

His ex-wife said he was arrogant and prickly, with "absolutely no natural courtesy or sympathy and no awareness of his lack of these qualities".

An ill-disguised sense of cunning has led to deep suspicion about his motives.

The son of a schoolmaster, Cook was born in Lanarkshire attending school in Glasgow.

An only child he had "a very secure and happy childhood" - living initially with his grandparents.

At school his favourite pursuits were the debating society and drama and he had an early interest in politics - becoming an avid reader of the New Statesman.

Soon involved in Labour politics, the young Cook headed to Edinburgh University where he began to make the colleagues and enemies who would accompany him on his rise through the party's ranks.

Then a bearded left-wing teacher, he cut his political teeth as Labour's candidate in the safe Tory seat of Edinburgh North.

After a defeat against the Earl of Dalkeith, he secured a seat on Edinburgh City Council - serving alongside the former Tory foreign secretary Malcolm Rifkind.

In the contest to select the candidate for the Labour seat of Edinburgh Central, Cook made enemies who remain with him to this day.

Using underhand tactics the Cook camp ran a spoiler against the then rising star George Foulkes - to this day a close ally of Gordon Brown.

"From that point onwards no-one trusted Robin. Many people in Edinburgh Labour politics never forgave him for that," said a leading member of the Edinburgh grassroots membership.

Once in parliament, Cook got off to a slow but steady start. Serving on the backbenches throughout the dying days of the Callaghan administration, he took his first frontbench post in 1980 when he became a Treasury spokesman.

After seeing boundary changes to his Edinburgh Central seat, Cook upped sticks and headed to the safe Labour territory of Livingston in 1983.

By 1987 he was an established operator, sitting in the shadow cabinet in possession of the health and social services portfolio.

As Labour ended its 18 years in opposition, Cook entered government as foreign secretary - a job which was snatched back when he was effectively demoted in the reshuffle following Tony Blair's second landslide victory.

"I thoroughly enjoyed being foreign secretary," he said last September.

For Cook, the decision was a cruel blow. Even then he considered resigning rather than take a reduced role in government.

Since being shunted into the job of Commons leader, Cook has attempted to carve out a distinct role for himself.

Through Commons modernisation he attempted to cement relations with the Labour backbenches.

On Lords reform, he pushed against Blairite cabinet colleagues including David Blunkett, Derry Irvine and John Prescott.

But for many it will be Cook's private life that remains the most vivid illustration of the man behind the public persona.

After an adulterous affair with his secretary, Gaynor Regan, Cook was forced to dump his wife in the departure lounge of Heathrow airport after a phonecall from Alastair Campbell.

As the recriminations of the split spilled out into the open, allegations of a heavy drinking, depressive and bitter man emerged.

In an explosive account of their 30-year marriage, Margaret Cook accused her husband - who once quipped that he was too ugly to become prime minister - of taking six lovers.

She said he drank heavily throughout Labour's wilderness years - and in 1987 was found passed out on the floor of a hotel with a brandy bottle.

Asked what he would do if Margaret committed suicide following the split, the then foreign secretary responded: "I should of course be sorry."

Mrs Cook also alleged her former husband was bitterly jealous of Gordon Brown, a long-time foe, and "hated" Peter Mandelson.

Since his demotion Cook is widely seen to have shifted back to the left.

The man who once said that there was a moral equivalence between the Soviet Union and the United States has let it be known he is deeply uneasy about a war with Iraq.

And from the backbenches he could easily become a totem pole for the growing number of MPs disillusioned with the direction Tony Blair is taking his party.