Election Focus: There has often been a mordant glee about Salmond, and these days it�s more visible than ever. But then in his 20 years at Westminster, the Mother of Parliaments has always had him down as the sour sound-bite outsider.

In one of the long, anonymous corridors of Portcullis House, Alex Salmond's researcher is trying to unlock the door to his Westminster office. "The electronic lock isn't reading the electronic key," she says wearily. We try again but it's futile. At which point the man himself emerges from the elevator, declaring, with scornful mirth, that we simply haven't got the knack. Then, taking the key, Salmond blows on it twice and, with a conjuror's flourish, he inserts it in the lock. Nothing. A security guard is summoned, and, in a swift, effortless gesture, he turns the master key. The door swings open in a second.

What are we to make of this vignette? Is Salmond's key trouble merely a glitch or one of Westminster's pesky little ways to cut a nationalist braggart down to size? "Aye," he says with feigned dudgeon. "If I had a car park space it would probably be gone by now. Next thing, the waste paper bin will disappear." We enter the room and settle quickly into the chairs; no point leaving anything to chance.

There has often been a mordant glee about Salmond, and these days it's more visible than ever. But then in his 20 years of representing Banff and Buchan at Westminster, the Mother of Parliaments has always had him down as the sour sound-bite outsider, a conceited opportunist who, on every big occasion, is on that patch of grass before the Commons, courting the media with apocalyptic warnings and a smirk. And he in turn has always regarded any Westminster brush off as perverse approval that he's effectively upset the apple cart.

"Hold on a minute," he says. "Haven't you noticed a change in me?" Not really. After all, this surge in the Scottish National Party's fortunes is hardly down to a gentling of Alex Salmond. Clearly its lead in many of the opinion polls for May's election suggests that the bold leader is not only upsetting his opponents' carts but pulverising their apples as well.

But let's get something straight once and for all: if May 4 becomes Salmond's victory day, is he or is he not going to stand down from Westminster? He sighs the deep sigh of someone who feels plagued by misinformation. "Listen, I'm taking nothing for granted. I'm standing for the Scottish Parliament, and, electorate willing, I hope to be there after May 4 when I shall devote myself to the Parliament at Holyrood, and stand down from Westminster at the next UK general election."

The precedent, he insists, is already set. "I'm doing exactly what Donald Dewar and Jim Wallace did. Incidentally I said all this in 2003 in an exclusive interview with The Herald's Catherine MacLeod. And, also incidentally, I don't remember anyone ever asking Donald Dewar that question. So, there's an element of double standards here." Of course, Salmond's incidentallys aren't incidental at all but retorts-in-waiting to make his enemies seem petty. Like all power-hungry politicians, he has spent his career perfecting the art of point-scoring. Even in his new "mature" persona he's not going to stop now.

Salmond's passion for politics began at his grandfather's knee in Linlithgow. "He was a tremendous man, the town plumber and local historian who gave me Blind Harry's tales about Bruce and Wallace." So, folklore ignited the romantic Scot in Salmond? "Well, there's a romantic element to national identity, but is it just that? No. In a globalised world you stand up for your own national identity by respecting those of other people. I hope that whatever else is said of me they'll say I pursued my Scottishness in that context."

But about all this business of maturing; does he feel he has gained gravitas? "Well, I'm glad you didn't use the word bottom', as in: Would you say, Mr Salmond, that you've acquired bottom?' I keep hearing that I've matured but actually I don't much care for the word. I think developed' is preferable." The image gurus have advised him to feel his pain. What pain are they talking about? "Oh, it's that phrase from Star TrekV where Spock goes through the whole film, telling people he can feel their pain. But what I'm learning is that sometimes you can be more effective by saying less rather than more."

That cryptic answer has its origins in an encounter with Robin Day. In 1987 Salmond, still an economist with the Royal Bank of Scotland, made his first appearance on Question Time, under Day's venerable but prickly chairmanship. "I think we were in Glasgow and I was on the panel with Denis Healey and Ken Clarke, and I was just having a great time. I was a young candidate trying to win a seat, and I had Denis cornered with what I thought were lots of good points. As a performer he was probably past his best by then but anyway, the audience was loving it, and then Day cut right across me and moved on to the next subject."

After the programme Day asked Salmond how he had enjoyed the experience. "I told him that I'd enjoyed it fine until he played that old pals' act with Denis Healey. Day asked what I meant, and I said: Well, you shouldn't have cut across me when I was pursuing a perfectly legitimate argument, and Healey was in deep trouble.'" Day reacted with unexpected avuncular concern, advising Salmond to go home and watch the recording, then call him afterwards if he still had a complaint. "So, when I'd done what he'd suggested I called him to say I had no complaint because I could see immediately why he'd cut me off. It was reaching a stage where I was becoming unreasonably aggressive, and if I'd carried on I'd have lost the audience. It has perhaps taken me a long time to appreciate that lesson."

Once at Westminster, Salmond wasn't slow "to back reluctantly into the limelight" in Jonathan Dimbleby's piquant phrase. For starters there was his infamous budget intervention of 1988. "We had three MPs down here then, and 644 others were pretty hostile. The SNP wasn't apparently going anywhere, the poll tax was being imposed, and nobody gave a stuff about the Scottish dimension. High Thatcherism was a seemingly indestructible force ruining the entire country. It was a cart that needed upsetting."

Salmond set to work, running at the Chancellor Nigel Lawson with such a battering ram of invective he could actually lip-read Lawson turning, in fury, to the Prime Minister and muttering "this is terrible". As a consequence the Banff and Buchan maverick knew the parliamentary establishment would be out for revenge, but in fact the incident made Salmond a celebrity. Or rather it gave him his first, addictive taste of notoriety.

"The Herald's editorial was fine in that it was balanced in its response, but The Scotsman's was really pompous, declaring that I was a disgrace to the country. Yet if the SNP was to gain any attention in those days we needed to do something out of the ordinary. Today we are in a different situation. I don't have to prove anything except to articulate a vision that transcends people's experience. Now, that's a big job and I don't want anything to get in the way of that message because the messenger is trying to be too clever. I mean, you cannot at the age of 52 be the boy wonder any longer."

Or a political hooligan? "Well, I don't agree that interrupting the Chancellor's budget - which was forcing a poll tax on the poor and giving tax cuts to the rich - was an act of hooliganism. It was a perfectly legitimate parliamentary tactic. The fact that you've got a generation of largely brain-dead politicians who've never read the rule book, is not my fault."

But that very anecdote confirms Salmond's natural instinct for jugular politics, a relish of the cut-and-thrust which he would surely miss on leaving Westminster? "I have always loved the Commons chamber. It's a fantastic debating arena, deliberately small in scale to intensify a sense of theatre, and, of course, I'd miss its adversarial vigour. But the Scottish chamber has a lot going for it, and I shall learn to love it, too, because I know the atmosphere can be made to dance."

After Gordon Brown and John Reid, Salmond is one of the most recognisable Scottish politicians in Britain. But even with that level of exposure he remains an enigma. Not a shy man but a private one who has managed successfully to shield his personal life from any intrusive glare. Someone, then, whom we don't entirely know. "Oh, I think you under-rate how folk get a feel for a person. Do they know every detail about me? Probably not, but there's a characteristic Scottish reserve which means you don't go around describing yourself or revealing your innermost thoughts, and I don't think that's a bad thing. One of my objections to this Prime Minister - a dreadful man incidentally - is the way he wears his religion on his sleeve when it suits him."

Salmond is equally scathing about the Blairite dauphin, David Miliband. "I saw him on Question Time where he was defending the Prime Minister against an incredibly hostile audience. And in considerable vexation he told them: In six months you'll be wanting Tony Blair back again.'"

As Salmond recalls it, David Dimbleby, the chairman, responded immediately by asking if that meant Gordon Brown would enjoy no prime ministerial honeymoon whatsoever. "I could see Miliband's eyes go as he realised his bright, shiny, perfect career had just come shuddering to the cliff edge. Gordon would be watching, and Gordon does not forget."

So, what should the Environment Secretary do now? "If I were Miliband I would stand for the Labour leadership because he will never be forgiven for that moment when he betrayed his thinking." And could he win? "No. But by running he'd be in a better position because if he doesn't stand he'll get Northern Ireland."

We reflect on Tony Blair's reluctance to leave the stage. "He should have taken a bit of advice from me and maybe he could have made a comeback. As it is, I'm thinking of offering my know-how to Charles Kennedy and William Hague." Shouldn't he be concentrating on his own comeback chances? "What do you mean, comeback'? I am back. I'm back."

Well, not quite. He hasn't yet made Holyrood dance to his tune. And, as a man of options, Alex Salmond might still find it useful to get that dodgy Westminster key sorted out.