The Saturday Profile: Lord Jenkins of Hillhead, om - The master code-breaker

Roy Jenkins spent much of the last war as a code-breaker at Bletchley Park, seeking to decipher top secret German signals. It was the most frustrating mental experience of his life, he says: "Particularly as the act of trying almost physically hurt one's brain, which became distinctly raw if it was not relieved by the catharsis of achievement."

At East Hendred, his Oxfordshire country house not far from Bletchley, Lord Jenkins has been going through something of a similar exercise over the past year. He has been attempting to navigate through the fiendish complexities of different voting systems - from the pure PR of the single transferable vote, to the alternative vote and many arcane combinations in between. That and the need to come up with a politically acceptable package has given Jenkins more pain in the brain.

But when his report is published next week, it will certainly be an elegant and persuasive piece of writing. For Jenkins has the gift of the pen. He has spent many hours, in a favourite phrase, titivating the text. One member of his committee says it will be the best written public document since Sir Ernest Gower's Royal Commission on Capital Punishment in 1953: high praise, as Sir Ernest also wrote the standard works on the use of English.

The report will propel Jenkins back into a favoured bathing-place: the limelight. But, at the age of nearly 79, the Rt Hon Lord Jenkins of Hillhead OM still retains a singular capacity for calling forth vitriol from his many enemies, on both the right and the left. They accuse him of class betrayal, Europhilia, arrogance and snobbery. But his image as a claret- quaffing, duchess-loving Establishment pillar misses many aspects of the man.

Jenkins has never been a Tory; he retains libertarian and internationalist instincts; he is something of a political gambler; and he has many personal eccentricities. As a politician with a hinterland, he is a prizewinning historian, and his memoirs were compellingly candid. He also has a powerful intuitive sense. His friend Lord Annan describes it using the German word, fingerspitzengefuhl: he feels things through his finger tips. He remains a figure of pervasive, if discreet, power and influence - a member of all the most select political clubs (the rules of one state: "the names of the Executive Committee shall be wrapped in impenetrable mystery"). And he is a mentor to Tony Blair.

When Blair first came to lunch at East Hendred, according to those present, the new Labour leader hung on the old statesman's words. Jenkins both helped augment Blair's sense of history, and familiarised him in the ways of modern Whitehall. The two men and their wives have dined together every few months. And Jenkins's official biographer, Andrew Adonis, has gone to work in No 10.

It would be to devalue the relationship to describe Jenkins as the Prime Minister's Woodrow Wyatt. They talk far less frequently on the telephone than Mrs T did to the old Tote man, with Blair normally initiating the call. But there is something of the same level of easy intimacy between the two men. "I like Tony Blair," says Jenkins. "I find him engaging - he is not too serious, not politically obsessed."

Blair knew that when he appointed Jenkins to recommend a PR system, he was choosing someone fascinated by figures. "I have been obsessed with numbers since I was a boy," says Jenkins. "I am not a higher mathematician, I am an arithmetician - a simple numerologist."

Early mornings at East Hendred offer bizarre evidence of this. Although he is surrounded by picturesque countryside, Jenkins chooses to take his pre-breakfast walk on his tennis court. He marches round and across the court in what he calls "an elaborate series of zig-zags". It is surreal to watch, but he explains it logically: "I walk for exactly 45 minutes: shorter would be too short and longer would consume too much time."

He keeps lists of the exact number of words he writes every day, and used to enjoy swapping railway timetables and cricket statistics with Harold Wilson in No 10. One of his former civil servants says that Jenkins was the only minister he had ever worked for who knew exactly how long it took for the main traffic lights to change in every major city in Britain.

You could almost call him an anorak - except that Jenkins would scarcely recognise such a garment, still less be able to pronounce it. Harold Macmillan is once said to have asked about the young Roy Jenkins: "Who is that grand fellow who makes me feel so common?"

Yet Jenkins was not born to the purple. And much of the criticism of him stems from a peculiarly English resentment of people who move out of their class. He grew up in south Wales, the only child of a coalminer. But Arthur Jenkins was an unusual miner. He studied at the Sorbonne in Paris, and at Ruskin College, Oxford, becoming a union leader, then a Labour MP.

Jenkins claims that his father had a greater influence on him socially than his mother, even though she was locally nicknamed "the Duchess": "Insofar as some people think I've got slightly grand, Whiggish tastes - they came more from him than from her."

To his father's delight, the Abersychan grammar school boy won a place at Balliol, where one of his tutors described him as "nature's Old Etonian". There, Jenkins first developed the voice - once described as like gargling in treacle - that would lay him open to ridicule in later years. But Jenkins says: "A whole variety of people - like the old Lord Salisbury - haven't been able to pronounce their Rs very ruggedly; that's perhaps a word I oughtn't to use too much," he adds ruefully. Jenkins took a first in politics, philosophy and economics. His history tutor had told him: "I am not sure how much you know, but you write it in a fine style - which I couldn't teach you, and which will be of more value to you than anything I could."

He was still at Oxford when he met the woman to whom he has now been married for over 50 years. Jennifer Morris was a Cambridge undergraduate from a professional family. She says of him: "Roy has always been the most engaging companion I've ever known, with many other attractions, too. It has always been better to be with him than with anybody else."

His Balliol connections ensured that Jenkins was recruited into Army intelligence during the war. By 1948 he had become an MP, and soon fell under the spell of the right-wing Labour leader, Hugh Gaitskell. "Hugh was the one person in politics I have not merely liked, but have loved. He really did have an inspirational effect on me as a leader." In the internecine party battles of the Fifties, the Gaitskellites prefigured New Labour; they wanted to ensure the regular election of centre-left, social democratic governments.

When Harold Wilson became Labour leader, after Gaitskell's sudden death in 1963, Jenkins thought of leaving politics altogether. But, within three years, he had became minister for the swinging Sixties in the Wilson government. As a young Home Secretary, he encouraged radical reforms of our social and sexual laws. Divorce was made easier, homosexuality and abortion were legalised, and theatre censorship was abolished altogether.

"I am a libertarian, and I was trying to make Britain a more liberal and open society," says Jenkins. He was regularly tipped as a future Labour prime minister in the Sixties. As chancellor, he revived the economy after the trauma of devaluation. But there were many in his party who deeply distrusted Jenkins's lifestyle. Wilson was later to say: "Roy is a very impressive figure with a lot of friends and social contacts. But he still felt that it was all like Asquith's day, where everything is done over a rather lush dinner table with good claret. But I never thought the Labour party could be run on the basis of dinner parties. I hardly had any at Downing Street - a sandwich occasionally."

When Wilson himself suddenly resigned as prime minister in 1976, Jenkins stood for the leadership. But, by then, he had become increasingly disillusioned with Labour: and the left's charge sheet of Jenkins's crimes against the party included his austere regime at the Treasury and his voting with the Heath government in favour of entry into Europe. He came third, behind Callaghan and Foot.

He soon left to become president of the European Commission in Brussels, where he was soon nicknamed "Le Roi Jean Quinze". He presented an incongruous spectacle when he appeared as a jogger in the Parc Cinquantenaire smoking a cigar. As president, he relaunched the idea of European Monetary Union - to which he remains totally committed.

But he was back in Britain after only four years, with an ambitious plan to break the mould of two-party politics: "I thought the Labour party had got itself into an appalling mess. I didn't in the least like Thatcherite Conservatism, and I thought there ought to be a third route." It was a phrase he used long before Blair ever talked of the Third Way. The Social Democratic Party that Jenkins had helped to create soared to 50 per cent in the opinion polls.

Yet, from the beginning, the new party contained the seeds of its own destruction. "Roy saw the SDP as a disposable vehicle for his ambition to become prime minister," says its co-founder, Dr David Owen. "Nonsense," replies Jenkins. "If anyone disposed of the SDP it was David Owen."

The Labour left claims the SDP's only achievement was to keep Mrs Thatcher in power for a decade. Jenkins says the shock effect of the SDP caused the Labour party to reform itself: "I think the Blair Labour party owes a great deal to the SDP." And he pays Blair the ultimate compliment, by calling him the best Labour party leader since his idol, Hugh Gaitskell.

As he completes the task that Blair has given him, the grand old man of British politics likes to relax with a game of croquet, where he demonstrates a sharp eye for angles and a ruthless instinct. "The object of the game," he told me, "is to keep your own two balls together, and separate your opponent's balls." It is a trick he will be trying to pull off next week when he presents his committee's recommendations.

If he can come up with a version of PR that reconciles the Cabinet ultras, and wins public approval while isolating the enemies of electoral reform, Lord Jenkins could guarantee himself the permanent place he so desires in our history.

For such a system could offer the prize that he has dreamt of since his friend Tony Blair was a toddler: to make Britain safe for social democracy, and turn the Tories into the natural party of opposition.

Life Story

Full Title: Baron Jenkins of Hillhead of Pontypool in the County of Gwent, OM, PC, Chancellor of the University of Oxford since 1987.

Vital statistics: Born Roy Harris Jenkins, 11 November 1920, son of Arthur Jenkins, Labour Welsh

mining MP.

Education: Abersychan Grammar School, University College Cardiff, Balliol College Oxford. First in PPE.

Marriage: Jennifer Morris, 1945, two sons and a daughter.

Public offices: Minister of Aviation, 1964-5; Home Secretary, 1965-67, 1974-76; Chancellor

of the Exchequer, 1967-1970; President of the European Commission, 1977- 81.

The "Claret" question: prefers St Emilion to Medoc. Best love is Chateau Lafite 1961 and 1966.

Nickname: "The Great Pooh-Bah" (P Ashdown). "Smoothy Chops" (H Wilson).

Old animosities: "The only thing Woy ever fought for was a table for two at the Mirabelle." (former Labour colleague).