Outside the office of Peter Lyburn, Conservative candidate for Perth and North Perthshire, is a tiny private aircraft, visible from his desk in the Scottish spring sunshine. Given the geography of this vast, rural constituency - which stretches from the town of Perth, 40 miles north of Edinburgh, across swaths of agricultural land and up to the Highlands - an aeroplane might not be a bad way to get to some voters. But when Lyburn appears outside the office - a couple of rooms in the control tower of Perth's small, non-commercial airport - it is in something less ostentatious.
His saloon car parked outside, the 26-year-old candidate for the Tories' most winnable seat in Scotland bounds into the room, eating an ice cream. He is confident of his chances of winning the seat, which the SNP holds by a margin of just 1,521 votes. He and his team started their campaign early - 18 months ago, he explains - and these busy final days are being run "almost like a military operation". Today's schedule includes a visit to a Perth care home to meet Andrew Lansley, who is in Scotland for the day. "We don't want to keep the shadow health secretary waiting," Lyburn says as we head for the car. But once we arrive in town, without a map, we can't find the right street. We decide to walk, but the elderly couple we ask for directions don't know either. When, with the help of an iPhone and Google Maps, we finally work out where to go, it's so far away that we have to return to the car and drive.
Unusually young and competing for a prominent marginal seat, Lyburn has attracted more attention than the average candidate. But then in most Scottish constituencies, Conservative candidates don't come in for scrutiny at all: what would be the point? At Westminster, Labour has by far the most Scottish seats; the popularity of both the party and its Fife-born leader is holding up. The SNP leads Scotland's minority government at Holyrood, and presents its Westminster candidates as a necessary buffer to protect Scottish interests from "the London parties". This argument has kept it in second place in the opinion polls, though lagging far behind Labour, to which the Nationalists tend to lose support in Westminster elections. As a result, the battles being fought in SNP-Labour marginals, such as the seat bordering Lyburn's, Ochil and South Perthshire, have become even tougher.
The Conservatives have only one Scottish MP, David Mundell in Dumfriesshire, Clydesdale and Tweeddale; David Cameron has conceded that most Tories north of the border have little or no chance of being elected. In some seats, they are fourth, or even fifth, in line. But as polling day draws nearer, and the widely predicted Conservative majority starts to look less and less inevitable, every marginal is becoming more important to the Tories, even in Scotland. The area that now comprises the Perth and North Perthshire seat has a long history of supporting the Conservatives: it has been SNP-held since 1995, but for almost all of the 20th century, it returned a Tory MP.
The half-decade Cameron has spent deodorising the Conservatives has had little impact in Scotland: the proportion of Scots willing to vote Tory has stuck resolutely at between 15 and 20 per cent since 2005. "Partly, it's because [the Conservatives] no longer have a strong hold in Scottish politics," explains Nicola McEwen, co-director of Edinburgh University's Institute of Governance. "If there is apathy towards Labour, ordisappointment, it's not going to benefit the Conservatives - it's going to go elsewhere, mainly. But also, one of the issues that is quite important for Scottish voters is which party can best represent them in the UK. And the Conservatives seem not to be able to do that."
However, at this general election, for the first time since 1992, it looks as if the Tories might return more than one Scottish seat. That's not to say there has been a significant shift in Scottish politics. Nobody expects the party to win the 11 seats it has set its sights on; Peter Kellner, of the polling organisation YouGov, is more generous than most in suggesting that the Tories might feasibly add seven seats to their existing one, but points out that "gains of one or two are more likely".
Cameron himself is yet to make headway with most Scots, McEwen says. "I don't think he gets the same reaction as Margaret Thatcher, for instance, but there's no sign that he is especially popular, or turning things around for Scotland."
There is one significant change. In Scotland before 2005, not even Conservatives liked the Conservatives: the Scottish party worked hard under its leader David McLetchie to develop a moderate, "One Nation" identity at Holyrood that was distinct from Michael Howard's British Conservatives. With Cameron in charge, that divide has disappeared. "They're much more comfortable with the 'compassionate Conservative' identity being nurtured just now," McEwen says.
Lyburn is the perfect example of a Scot "energised in the party by David Cameron". He is such a textbook Cameroon, he could have been generated in a lab somewhere deep inside CCHQ. "We need to focus on the bottom 10 per cent of society," he tells me. "David Cameron calls it progressive ends by conservative means, and I agree with him 110 per cent."
He's a local candidate, having grown up on a farm outside nearby Coupar Angus, and has the requisite green credentials, after three years working for a recycling firm owned by the Scottish multimillionaire entrepreneur Angus MacDonald. Indeed, on his first foray into politics as the Scottish parliamentary candidate for Dunfermline West in 2007, Tatler magazine tipped him as a future environment secretary - as well as "top Tory totty". "He looks like a Conservative candidate," remarks the Scottish political commentator David Torrance. "He's got this mass of very Tory hair."
Lyburn is trying to sell the notion of a refreshed Conservative Party, with new candidates like himself. "What we're trying to get across to people is -look at our list of 11 seats. If you're in one of them, don't think you're the only person in your street who thinks the way you do," he says. Yet he denies there is any stigma attached to voting Tory in Scotland.
Lyburn tells me that his previous political campaign in Dunfermline shook the "stereotypical Tory boy" out of him. But at a public meeting that evening in the village of Scone, he tells a polite and attentive gathering of 25 or so that "there is a real and present danger of young people growing up without a 'get out and work' attitude". He relates his own experiences: if his dad hadn't got him up in the mornings to help out around the farm, he would have stayed in bed. Apparently this is the sort of discipline broken Britain needs.
Lyburn is hoping that Scots will respect the "grown-up politics" of Budget rebalancing - including significant cuts to the public sector, which employs a quarter of Scotland's workforce. He may be right, in a sense: despite Alistair Darling's Budget announcement that spending in Scotland is to fall by £400m, 60 per cent of the country's voters still back a Labour government. But the SNP is targeting both the Tories and Labour with one line: "More Nats means less cuts."
Perth's SNP MP, Pete Wishart, is presenting an even less complicated message on the doorstep. Dressed in a coat with a faint check - Black Watch, the regiment founded in the area and reduced to battalion status by Labour, with Conservative support - he tells people repeatedly: "It's us or the Tories in this constituency." Several respond: "Anybody but the Tories."
In this part of the town, there is support for just about everyone else. A few say they're SNP voters; about as many seem unlikely to vote at all. A middle-aged Labour supporter, recently made redundant by Network Rail, agrees to think about the SNP as a tactical anti-Tory vote, while another of about the same age, a builder, is agitated about Perth's Polish population. But it is the BNP's world-view, not the Conservatives' promised cap on immigration, that has caught his eye. "They aren't right on everything, but they've got the right idea on some things. Haven't they?"
Wishart may be working to keep the Conservatives out of his constituency, but he says the SNP's ultimate goal, independence for Scotland, would be served well by a Tory government in Westminster. "It would be an absolute disaster for Scotland," he says, but "this provides other opportunities and contexts. There is a big constitutional question for David Cameron if he is returned as prime minister with only a few MPs for Scotland. [But] I'm not bothered if Brown or Cameron wins. I want Perthshire to win, that's my agenda."
Like the Liberal Democrats, the SNP argues that the two main parties are the same: "They're both committed to cutting Scotland's budget."
Officially, the SNP could hardly be seen to support a Conservative government at Westminster. During general elections, independence takes a back seat, and it would be perverse for the Nationalists to campaign as Scotland's "local champions" while backing a party with so little Scottish support, especially now that Cameron has ruled out the possibility of negotiating with the SNP in return for support in a hung parliament. But a Labour win - or even a good return - may have grave consequences for the SNP. There will be a Scottish parliamentary election next year, and a positive general election for Labour, which has just one seat fewer than the SNP in the Scottish Parliament, should lead to a boost at Holyrood.
Dodging left and right
A hung parliament, meanwhile, would allow the SNP to "Scotland-proof any piece of legislation", as Wishart puts it. But while the SNP is popular - more so than it was in 2005 - it looks unlikely to add many, if any, seats to its present haul of seven. Appealing to the anti-Tory vote is the more obvious route to popularity.
The same tactic is in use in neighbouring Ochil and South Perthshire, another large, rural constituency. But here - a seat that Labour holds by a mere 688 votes, and that the SNP considers to be its top target - it's not the Nationalists who are using it but the incumbents, who are fighting their campaign on a UK platform.
However, the SNP's Annabelle Ewing is out fighting her own negative campaign. In the streets of central Alloa, which have been thrown into chaos by a major redevelopment project, her focus is the failures of the local Labour council, which has fallen £9m into debt. Swaddled in an enormous yellow overcoat, Ewing is a consummate politician - perhaps unsurprisingly: she is the daughter of the former SNP president Winnie Ewing, and her brother is an MSP.
As we stroll through the Continental food market in the town high street, Ewing stops to speak only to shoppers, not stallholders, most of whom are from outside the constituency, so "they're not voters".
What she has to say plays, mostly, very well. Closures of public toilets and local halls have angered residents, and many of them are quite prepared to leave the blame where Ewing lays it, at Labour's door, although one elderly lady interjects "and the SNP at Holyrood". A passer-by in a baseball cap with a Scottish flag on it tells Ewing that he doesn't believe in independence: it's not the English he's worried about, it's "the Arabs and the Yanks". But he speaks warmly about George Reid, a former SNP MP and MSP for the area, and as he walks off he tells her: "Aye, I'll vote for you. That's not a problem."
Ewing emphasises the SNP's support for business and its rejection of Labour's planned National Insurance increase - "another burden that small business, in particular, does not need". The SNP has long stressed it is the party of Scottish enterprise, although its leader Alex Salmond, once an economist at the Royal Bank of Scotland, has had to abandon his vision of Scotland as part of an "arc of prosperity" stretching from Ireland to Iceland. In this constituency particularly, it may be a canny card to play. Like Perth and North Perthshire, Ochil includes a large pocket of Tory voters, who may choose to vote tactically for the SNP to keep the Labour incumbent, Gordon Banks, from holding on to the seat. Asked about the party's ideological positioning, Ewing dodges the question of left or right: she is concerned only with "protecting Scotland's interests".
Meanwhile, Banks is taking an approach oddly reminiscent of Pete Wishart's. "I don't care what the SNP do, I don't care what the Tories do," the MP says. "What concerns me is my tactics." And those are ultra-local. In keeping with most of Labour's national pledges, he is offering his constituents more of what he has given them so far: he promises to be "as open and available as I have been over the last five years", pointing out that he maintains two constituency offices - one in Alloa, one in Crieff - to make things easy for them.
An unscientific sample of voters in nearby Clackmannan, a historically Labour-supporting area of the seat, suggests it may not be enough. Surrounded by a team of canvassers in bright red Scottish Labour cagoules, Banks makes an argument that is the same as the SNP's in Perth: can you stand to see the Tories win?
A woman on her way out into the evening sunshine tells him that "Labour have let me down so far" - on housing, on immigration - and adds, "I've written to yourself." Banks talks to her at length about her worries, then reminds her that a vote for the SNP is an open back door for the Tories. "I didn't like what they did under Maggie," she concedes.
As we walk on, Banks explains that this argument is not what it was. A woman in a football shirt takes one look at Banks and tells him she won't be voting - she is "not very impressed generally" by politicians. One campaigner approaches to say that they've just met a Tory. "Not a very nice one," he adds glumly, shifting the shoulder bag of leaflets resting against his hip. Tory voters, Banks remarks with resignation, "are no longer reluctant to tell you so".
But perhaps there is a positive side to this for Labour. With the peculiarities of Scottish politics, it is possible - just - that the tiny uptick in the Tories' Scottish reputation could work in Banks's favour. The Conservatives are now claiming to have the backing of 50 Scottish companies and business leaders over National Insurance - including that of Lyburn's former boss Angus MacDonald. If the Scottish Tories recast themselves as the party of Scottish business, the Conservative candidate for Ochil and South Perthshire may drain away a few of Ewing's votes. And if that happens, Gordon Brown may just find himself with one seat to thank David Cameron for.