We have just asked Sir Menzies Campbell when he last poked someone. The face of the Liberal Democrat leader registers utter astonishment, a flush of alarm then a hint of anger. Poking is, we hurriedly assure him, a technical term, from Facebook, which he was the first party leader to sign up to.

“Ah. I was encouraged to do that . . . I’ve got someone who monitors it for me because there are quite a lot of other things going on,” he says.

Indeed there are. In the year and a half since Sir Menzies became leader, his party’s ratings have remained low, leading to mutterings about whether he is too old for the new generation of voters. There are even suggestions that his predecessor, Charles Kennedy, with his Have I Got News For Youpopular appeal, might make a comeback. Sir Menzies is expected to face a rough ride at the party’s annual conference next weekend.

You cannot accuse Sir Menzies, or at least his aides, of failing to recognise the problem. On the table between us lies a briefing sheet for the barrister, Olympic athlete, cancer survivor and the only senior MP to have read Iraq right, from the start.

“You should assume,” the adviser wrote, “that Alice and Helen are coming into the room expecting to find someone who is old, tired and lacking in the vision that leadership requires. For the interview you need to bear this in mind by being positive, purposeful and by being relaxed when they ask personal questions.”

All senior politicians get memos like this before interviews; few are unguarded enough to leave them in view. Sir Menzies, who is 66, holds to an ideal of principled politics, and principled journalists too, who wouldn’t stoop to reproducing a private note. Whether that can succeed – especially for a third party, and in our personality-obsessed age – he has yet to prove. “People do attach importance to leadership, but I think consistency and reliability are important. I think there is a move away from spin. I think there’s a move away from personality.”

But critics would say that the hard work the Lib Dems have done on policy this year – such as tougher border controls with an amnesty for some immigrants and serious plans for a carbon-neutral Britain by 2050 – has been for nought, if the leader is not keen on the zanier publicity stunts that grab headlines. Could he become a bit flashier to raise their profile?

“You can’t be what you’re not. The public know very, very quickly when people are playing a role that they are not,” he says.

With this in mind, we press ahead with our “personal questions”, with some surprising results. First, his marriage to an older single mother in a whirlwind romance. He began the tale at a party, in a Scottish castle, and his eyes started to gleam: “There was a fireplace about the length of this room. And there standing at the fireplace was this gorgeous creature. We danced all night. It was Friday the 13th of March, and we got married on Friday 12th of June. So we met, engaged and married in three months. My wife said she held her nose and jumped.”

Was that a bit sudden? “Sudden for someone as serious as me?” he said, smiling. No, we meant to take on a five-year-old boy at the age of 29? “I’m choosing my words with some care because I’m exceptionally fond of him and he, I think, is exceptionally fond of me. But I never set out to replace his father. His father was charming, quixotic, and I hope you might describe me as charming, but I don’t think you’d ever describe me as quixotic.”

His stepson never called him Dad, preferring, as everyone does, “Ming”.

“But then my grandsons call me Ming. No question of gramp. I mean everyone calls me Ming. I’ve been resisting it all my life, but I may have reached a point now to stop.”

The nickname hails from his days as a rugby player: “Ming on the wing – it’s too easy isn’t it?”

He says: “I don’t like being Sir Ming, because I think it sounds silly. I’d rather people just dropped the Sir altogether and called me Ming Campbell.”

Ming and Elspeth have been married for about 40 years, and their relationship is very much of their generation. She cooks, he knows but three recipes from his “bachelor” days (lamb chops, fillet steak and poached fish). She, mostly, shops and cleans, but married him on condition that she didn’t have to iron – a pile of shirts lies in the corner of his Commons office, back from the laundry.

When did he last watch a television programme that wasn’t about current affairs? He is submitting his fine brain to such shallow lines of inquiry so graciously, it is almost embarrassing. But he pauses to think: he watches a lot of sport, he likes The Bill and vintage detective shows, and his wife makes him watch Coronation Street, because her academic interest in it earned her a first-class degree from the Open University.

“Strong women, weak men,” is his verdict. “Rita is much tougher than Norris. And Deirdre’s much tougher than Ken. If you look, that’s the kind of genre of Coronation Street.”

He and Elspeth never had children of their own; we wondered whether they had considered it. “It never happened and I’m entirely philosophical about that. Life is not empty. We have three energetic grandsons who keep us extremely busy.”

We now, understandably, reach the limits of Ming’s ability to bear intrusive questioning. We ask instead what he thought of modern politicians’ attempts to influence all sorts of personal issues, including women’s decisions about marriage, children and work.

“Might I take issue?” he asks politely but with steel. “Look at the way in which the role of women has changed. Look at the extent to which, unheard of only a few years ago, there are women who are storing their eggs because, for the moment, they want to concentrate on a career and they haven’t found someone that they want to spend the rest of their lives with.

“And that’s free personal choice. Just as our free personal choice did not result in any children. I can’t emphasise enough my sense that these are whole areas of life that politicians should keep out of. And other than supporting the family, however it’s constituted, then I believe that very strongly.”

It is a classic liberal stance, and in keeping with his sense that private lives – his own included – are not for career exploitation. It is a view he shares with Gordon Brown. “Gordon Brown has brought a new seriousness to politics. And I don’t think I’m saying anything my handlers would object to when I say that I’d find a new seriousness in politics easier to cope with. But I think I’m not alone in that.”

He has known the Prime Minister for three decades, since Mr Brown was a television researcher, booking Sir Menzies, then chairman of the Scottish Liberal Party. Their friendship is a tricky subject. “Scotland’s this political village. We’re friends. I mean there’s absolutely no dispute about that. But the fact that we are friends does not mean to say we share the same political beliefs any more than the fact that [the Scottish Conservative] Malcolm Rifkind and his wife may come to lunch with us means that I share Malcolm’s beliefs.”

He and Mr Brown represent neighbouring constituencies, love rugby, came from modest homes, and were good friends with the late Scottish Labour patriarchs Donald Dewar and John Smith. Both he and Mr Brown believe that the power of their intellects will win out despite the more populist charisma of their junior, David Cameron.

“Age is less and less important and judgment is more and more important. Now, I’m not saying young people don’t have good judgment,” he says. “If it was left to the young people of this country as to whether or not we should take military action against Saddam Hussein, we’d’ve got a pretty resounding no, wouldn’t we? More, it is as unacceptable to say that someone who is older can’t understand what motivates people of a different age, as it would be to say that no young person has got the judgment to decide whether or not we should take military action against a dictator.”

Does he find it offensive when people poke fun at him just for being old? “You need a thick skin in this business.” But it hasn’t been the easiest year. He replies: “No, but listen, life isn’t easy, life’s not fair. I worked that out a long time ago. And what you do is you set your objectives and you bend might and main, strain every sinew – sounds quite Churchillian – to achieve them. And that’s what I’m doing. That’s what I’ve had to do all my life.”

He says that he will lead his party into the next Parliament, but are there any circumstances in which he would bow out? “I can’t envisage any.”

He must must be relieved that our time is up, but we have saved the worst question to last: does he know any jokes? He gives us a couple of self-mocking “Lib Dem” ones. Any others? “I know lots of jokes, not all of them are entirely suitable for delicate ears.”

We don’t mind if it’s dirty, we protest, but he just laughs. “My parents would be astounded at the notion that I might tell a dirty joke to two women.”

Courteous to the end, it is the only question that he does not answer with open intelligence. Chat-show Charlie he is not, but do we want our leaders to be serious or silly? Thoughtful or flashy? The Liberal Democrats may be about to find out.

Going the distance

Born May 22, 1941

Family Married Elspeth, Lady Suttie, in 1970

Education Hillhead High School, Glasgow and Stanford universities

Sports 1964 Sprinted for Great Britain in Olympic Games in Tokyo

Career In 1968 he was admitted to the Faculty of Advocates. He continued his passion for politics and became chairman of Scottish Liberals in 1975. In 1982 he was made a QC and in 1987 elected MP for North East Fife. He is respected, by all parties, for his insights on foreign affairs and in 2001 he became the Lib Dems’ Foreign Affairs spokesman. Two years later he was appointed deputy leader. Knighted in 2004 and succeeded Charles Kennedy as leader last year

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