Stockton South is one of the most marginal constituencies in the country and could define the General Election. Chris Webber found out more.

SOME moments on some election nights sear themselves in the memory and seem to define the drama of the night forever.

In the 1992 General Election there was Basildon, the Tory victory that signalled a big, unexpected win for John Major's Conservatives and in 1997 millions asked each other if they 'stayed up for Portillo,' the moment in the early hours of the morning when Government minister Michael Portillo lost his seat, indicating the sheer scale of Tony Blair and Labour's victory.

Stockton South, which should be an absolutely nailed on 'gain' for Labour, could easily provide enough drama to be the defining moment of the 2015 General Election if, as many think, 31-year-old Conservative MP James Wharton manages to hold on to the ultra-marginal and the Tories end up top dogs.

Some predict this privately-educated MP might even increase his majority in what is one of only two really marginal seats in the whole of the North-East, the other being Berwick where veteran Liberal Democrat Alan Beith is standing down.

If he does, and a Unite union poll in the constituency last November put Mr Wharton two points ahead of his rival Labour's Louise Baldock, it will be a major achievement. For Mr Wharton won by just 332 votes at the 2010 election making it the 19th most marginal seat in the country.

In any ordinary political cycle the natural weakening in the popularity of any incumbent Government would more or less guarantee a win for the other side and it is seventh on Labour's target list.

And yet this has not been an ordinary political cycle, a fact which appears to working in Mr Wharton's favour.

For a start the Liberal Democrat vote, which had been strong in the well-to-do Eaglescliffe and Yarm areas, appears to have collapsed. In the last election the Liberal Democrats secured 15 per cent of the vote but the Unite poll had the party on just three per cent. Conventional wisdom would have much of that vote automatically going to Labour, but in better off areas like Eaglescliffe that does not always necessarily follow, for example Conservatives took what had been Liberal Democrat seats in Cornwall at the last election despite a strong national showing from the Liberal Democrats. Other parties, like the Greens, are thought also to be picking up former Liberal Democrat votes.

Then there has been the rise of Ukip. Again, on the face of it, a rise in a right-wing might be considered bad news for any Conservative MP. However, Ukip is capable of taking traditional Labour votes, as evidenced by the fact the party came within just a few hundred votes of taking what was considered a safe Labour seat, Heywood and Middleton, in Greater Manchester in a by-election last year. Meanwhile Mr Wharton won a lot of publicity for his parliamentary bill for a referendum on EU membership, a policy strongly supported by Ukip, which appears to be helping him shore up the Eurosceptic vote.

Then there is the scale of Mr Wharton's financial support. His rival, Ms Baldock, estimates Mr Wharton has had at least four times the cash, about £200,000 to spend than she does herself. Conservative Party literature has poured through the doors of target voters.

The seat, in all its previous incarnations, has been volatile over the years. Labour came third in both 1983, when SDP candidate Ian Wrigglesworth won, and 1987 when Conservative Tim Devlin took the seat but then went to win a massive 55 per cent of the vote in 1997.

To be clear, Stockton South could easily turn red once again and at least one betting company has Labour as slight favourites. That earlier, Ashcroft, poll had Labour comfortably ahead and Ms Baldock, who was only two per cent behind in the Unite poll well within the 'margin of error', has devoted herself to campaigning full time for well over a year, pledging to knock on every single door in the constituency.

And yet you can feel the frustration in the Labour ranks in the constituency where they should be ahead. Prosperous by North-East standards, certainly, it still has a higher than average number of jobseeker claimants and strong, working class communities in Thornaby and the Oxbridge area of Stockton. As a blogger on the Labour List website said: "The seat is still eminently winnable for Labour. But it shouldn't really be doubt."

But it is in doubt. And if Labour don't win here, what chance becoming the biggest party come May 8?