The black elasticated arm support is just visible beneath the cuff of his dark blue suit. Not many people get a repetitive strain injury from shaking hands. But then not many people have shaken as many hands as Scotland’s first minister in the last two years.

Alex Salmond traversed Scotland many times over in his quest for a Yes vote on 18 September. And the next day, having attracted 45% of the vote, he announced his resignation. In two weeks' time, at his party’s annual conference in Perth, his deputy, Nicola Sturgeon, will be elected unopposed as his successor.

He made the decision to stand down only on the morning after the vote before, he confides, when we meet in a country house hotel 40 minutes from his Aberdeenshire home. “I’m old-fashioned enough to think that someone has to take responsibility for a major decision. And I’ve never had a problem with taking decisions, or been much of a man for prevarication.” And not much of a man for regrets about the campaign he fought, though it’s no secret there were tensions between SNP strategists and the umbrella Yes campaign.

What the poll did teach him, he says, was about other factors at play. The generational shift, with the under-40s voting Yes, and the over-55s saying No. Time, he reasoned, to let a new and younger leadership “blossom”. And time to focus swiftly on the vow – famous or notorious according to inclination – made by the three UK party leaders on the eve of the poll: more and “extensive” powers for the Holyrood parliament if the Scottish electorate resisted the siren call of a fully sovereign nation. Feet, he says, must now be held to the fire to ensure delivery.

The architects of that vow, of course, were not the three signatories; rather, it was former prime minister Gordon Brown who did the deal, with the Labour-supporting Daily Record featuring it on a striking front page.

Was Brown shafted by the prime minister? “Well, Gordon thinks he was, which is probably more relevant,” Salmond says. “He went within a matter of hours from the man who was writing David Cameron’s Scottish speeches two days before the vote, to the man who had no idea what was in the PM’s statement at 7am the morning after it. You wonder only that he was surprised. It is after all in the nature of the Tory beast.”

‘The pendulum (on the constitution) has swung very far. I don’t think it’s going to swing back’ … Alex Salmond during the Scottish referendum campaign. Photograph: Murdo MacLeod/Guardian

We met just before the startling events of recent days – the sudden resignation of Labour leader Johann Lamont, the subsequent resignation of her deputy, Anas Sarwar, and the emergence of the pugnacious Jim Murphy as Lamont’s likely successor. They have provoked a predictably robust public reaction: Salmond promptly described Labour as “a hotbed of factionalism and poisonous infighting – between factions in Scotland and London and within those factions themselves. That is the reality of what their new leader in Scotland will inherit and what they will be consumed by – rather than concentrating on the issues that matter to the people of Scotland.” And he is not above adding fuel to the flames: “And we now have the astonishing claims, reported in the New Statesman, that Jim Murphy was preparing to publish a list of Labour colleagues who were calling for Lamont’s sacking, a claim he must now answer.”

But Salmond himself has always excited strong opinions, from those who see him as Scotland’s most talented politician, to those who assured canvassers they “cannae stand that man”. Arguably that’s because his confidence can come over as arrogance: “Smart Alex” was not a soubriquet born of love. Before his 2011 triumph in the Scottish election, consultants urged him to avoid seeming smug. But such has been the demand for tickets to see his final hurrah that the last day of the conference has been moved to Glasgow’s Hydro arena. SNP membership has tripled since the referendum.

Now, having led his party for two periods of 10 years, with a four-year interlude at Westminster, speculation is rife that he will return to the Commons. He dances round the question before finally conceding: “I haven’t made up my mind. It’s for others as well to decide. The people who select candidates, for one. It’s a question of what is the most useful thing I can do to further the Scottish case.” A betting man – and Salmond is a high-profile one, and a tipster to boot – might conclude that his mind is already halfway down the M1. It certainly seemed so on Question Time last week, where he gave his “definitely maybe” a first public outing. He keeps more than half an eye on the Whitehall scene, noting with some asperity the current row between Cameron and the outgoing European Commission president about free movement of workers. “Señor Barroso, the seer of Europe when it was a question of Scotland’s membership, is now apparently ‘a half-baked Brussels bureaucrat’.”

Were he to plant his now-slimmer backside back on the green benches – he lost two and a half stone on the 5/2 diet during the campaign – he would pick his fights with care. As the SNP has long taken a self-denying ordinance and doesn’t vote on purely English matters, he has no problem in principle with English votes for English laws (or EVEL). “But it’s not always as straightforward as it seems. We voted against foundation hospitals because we thought that ultimately it would have a knock-on effect on the money available through the Barnett formula for the NHS in Scotland. Nobody introduces privatisation to put more money into the public purse! And we also voted against raising tuition fees, having failed to persuade a Labour government not to renege on its promise. So there are times when EVEL produces evil polices.”

We met just as the Smith commission, set up by Cameron to look at what new “extensive powers” might involve, was getting under way. Salmond admires Smith, but thinks there’s little hope of white smoke emerging “until the realities of the May election kick in. We have an unprecedented situation where all three main political leaders at Westminster are simultaneously unpopular. That’s unusual; normally when one is down the other is up. I think that makes it very difficult to see either Labour or the Conservatives winning an outright majority.”

His analysis of his fellow leaders is not charitable. Cameron, he suggests, had a good first year before becoming imprisoned by his right wing, losing control of events and party management. Miliband, he says, is more unelectable than Michael Foot, “and without any of Foot’s wonderful qualities or intelligence. He’s more unelectable than Neil Kinnock was; and Kinnock had considerable powers of oratory, and didn’t lack political courage.”

Unsurprisingly, he endorses Nicola Sturgeon’s attempt to have any referendum on European membership subject to the approval of each of the four home nations: “An in/out referendum in 2017 now seems inevitable, almost regardless of who wins next May. I don’t think the EU is perfect. Far from it. It badly needs change and reform. But I do believe – strongly – that our interests are best served by being in the EU. Nicola is therefore quite right to say that for the UK to leave the EU, each of the four constituent nations would have to vote to do so, not just the UK as a whole.”

In Salmond’s last Commons incarnation, he certainly made his presence felt, not least in a failed attempt to have Tony Blair impeached over the Iraq war. But he tells me that what will matter in May is not the personnel mustering under the SNP banner, but the numbers. “Westminster is ultimately always a numbers game. You can preach the sermon on the mount in there and still lose the vote. And whether or not that vow is redeemed will be down to numbers, too. Whether we have enough to hold the balance of power.”

Alex Salmond and his wife, Moira, on the night of the Scottish parliament general election in 2011. Photograph: David Moir/Reuters

If they do, coalition isn’t on the menu. At least, “not ever with the Tories. Labour? That might be different, but it’s not for me to decide. I’d only note from my own experience that you exert more influence outside coalitions.” And that influence could be considerable. A brace of polls this week suggested that Labour ructions could hand the SNP such a raft of seats that they could potentially hold the balance of power at Westminster. The referendum, in which 40% of Labour voted yes, has changed the Scottish game. It’s certainly Salmond’s view that “the pendulum (on the constitution) has swung very far. I don’t think it’s going to swing back.”

This is perhaps why I detected neither signs of terminal disappointment nor demob-happiness in the demeanour of a man who has fought for Scottish independence since his teens, and who thought, until a very late stage, that a historic victory was his. In part this is because of a strange phenomenon whereby the first minister is far from the only person to observe that “the winners are behaving like losers, and the losers like winners”. He insists his oft-quoted remark that referenda come along once in a political generation referred only to the gap between the one in 1979 and the next in 1997. “But that decision is not for me or any other politician. It is a matter for the Scottish voters if they decide to support a party which puts the idea forward. Who knows? Politics is always changing.”

Even if he has a second coming at Westminster, there are no guarantees his agenda will be followed. He will join a house preoccupied with a general election, a European referendum, the impact of Ukip, and not least, with the many permutations for English devolution that have emerged since Cameron’s declaration on 19 September that that goal was to be pursued in tandem with any additional powers for Holyrood. And, as he notes, decisions on how best to proceed in both the Smith commission and the Commons will be taken by his successor. The relationship with Sturgeon will undoubtedly alter as she moves into his chair.

But theirs has been an enduring partnership, one that celebrated a decade together this year. “Again, there may be intergenerational factors at play. I hesitate to draw any analogy with Ian Paisley and Martin McGuinness as the circumstances are so very different. But perhaps there’s something of an uncle-nephew thing, which worked for them as well as personal chemistry.” So while Alexander Elliot Anderson Salmond has undertaken not to be a back-seat driver, he is not a man likely to slip into the political shadows any time soon. However sylph-like his post-dietary self becomes.

Formal proceedings over, we repair for lunch with his famously private wife, Moira, a woman once his civil service boss, and his spouse of 33 years. Their banter suggests both a strong relationship, and that more than one opinion prevails in the domestic arena. In person, in private, he displays a congenial persona not always evident at the dispatch box.

Earlier, when the legacy question came up, Salmon flagged up free personal care for the elderly, no tuition fees, and all the other Scottish policies that travel far up the noses of English voters. All achieved, he reminds you, from the block grant and against the backcloth of austerity. During lunch, when he shamelessly steals forbidden chips, he has a rethink. “Actually, I believe the thing I’m most pleased to leave behind is a highly politically engaged Scottish electorate.”