Can the Tories really win the next general election?

It's rarely worth asking the question. Over the last 30 years, it's only really 1992 and 2010 where there was a genuine query over the result of a general election. But that's certainly not the case in 2015 when, some argue, we're faced with a battle unlike any we've ever had before.

The Conservatives face the unusual and undesirable prospect of being a governing party which has to increase its vote share to be returned to power with an overall majority. After a full period in office, parties very rarely manage to actually win more approval. Thatcher managed it in 1983, but had the small matter of the Falklands War to help her out. We don't know what the next 21 months have in store, but Cameron's probably not going to have to deal with anything as extreme as that.

It's not a great outlook for the Tories, but you wouldn't think that to look at the current ebullient mood of the Conservative party. Its grassroots activists and MPs are cock-a-hoop over recent positive economic news. Green shoots are now popping up all over the rubble of the financial crash and, in a couple of years, even living standards might start rising again. This is why the jovial atmosphere of the No 10 Rose Garden's summer barbeque, with the leader handing out burgers to his quiescent backbenchers,  has lingered all summer.

"The economy is the over-riding factor," Laurence Janta-Lipinski of pollsters YouGov says. People remain pessimistic right now, but the numbers are changing and by 2015, with firmer growth returning, the coalition's cling-on-and-hope strategy might actually pay off.

Tories are upbeat about the economy because it works both ways. The government gets the credit and Labour, even three years after leaving office, continues to get all the blame. Ed Miliband has struggled to shake off the public perception that the crash was all New Labour's fault. As a recent ICM poll showed, his and Ed Balls' economic competence ratings are not improving nearly as quickly as those of Cameron and George Osborne's. "If this continues, Labour has a problem," the LSE's Tony Travers says. "They have to get 38, 39, 40% to be certain of winning an outright majority."

There is an alternative. It's what's becoming known as the '35% strategy', in which Labour aims to shore up its core vote and attract just a few more from here and there to keep the Tories out of power. The logic behind this is astounding. It is based on the goal of securing Labour as the largest party in the next parliament, rather than as the outright winner. In 2010 the Conservatives' seven-point advantage over Labour (36% to 29%) was not enough for them to secure an overall majority over Gordon Brown. This suggests they need an eight-point swing in order to get Cameron into No 10 on his own. With Labour on 35%, the Tories would have to get around 39% to stand a chance of emerging in first place in a hung parliament. The problem for the Tory party is the chances of Labour being on 30% are virtually zero.

Labour's vote rests, to an extent which is uncomfortable for pretty much everyone, on the performance of the Liberal Democrats. Nick Clegg's party has shed at least ten per cent of its vote share since the 23% it notched up in the heady days of 2010. Of those, Labour are taking the lion's share – about four ex-Lib Dem voters to every one who switches to the Tories. "Ironically, the Tories need a strong Lib Dem party on a national basis," the psephologist and former MP Rob Hayward says. The Lib Dems are bound to lose seats to Labour in the north and Midlands, but the extent of the losses could be limited if the Lib Dems' tradition of strong performances by incumbents survives the trauma of government.

Hayward's analysis is questioned by Travers, who believes the Labour advantage in terms of seats resulting from a poor Lib Dem performance is outweighed by the potential gains against the Lib Dems in places like the south-west. Here the Conservatives are in second place to the Lib Dems across a number of seats. The question then becomes one of the Lib Dems' defensive qualities. Eastleigh, despite Ukip coming second, is a case in point.

Ah, Ukip. Another Nigel Farage-shaped spanner to throw into the works of a Cameron overall majority. "In midterm you get people expressing dissatisfaction," Janta-Lipinski says. He has a "strong suspicion" Ukip is the manifestation of exactly that. But how much will their vote be eroded? How much will voters find themselves splitting their votes between local authority elections and the general? And how much of a distorting effect will they have elsewhere in the country – in the metropolitan areas of the north against Labour, and against the Lib Dems in the non-conformist south-west? Right now, on all of these imponderables, it's far too early to say.

Until 2015 all the current polls tell us is simply that this is going to be a very tight election. You can read whatever you like into them – and if you're a particularly animated friend or enemy of Ed Miliband, for example – you probably already have – but you'll be making inferences based on very little. The first indications of the economy's true effect on this contest will come after the 2014 party conferences. There will be undecideds after that, but it is around that time the formation of the bulk of voters' views will begin to take place.

The most likely result right now has to be a hung parliament with Labour as the largest party. But there are so many unfamiliar factors at work in this volatile, unpredictable run-in to 2015 that we're in uncharted waters, with even the most experienced commentators left bewildered by the number of unprecedented scenarios all coming together. As the parties gather for their autumn conferences this year, they'll know their potential worst- and best-case scenarios are much further apart than usual. Welcome to another period of highly-charged, highly unpredictable politics. The stakes are getting higher and higher – and we haven't got a clue who's going to win.