@FootballFan:
What's wrong with McDonald's? I personally work there on weekends... it's a much better job than you expect, mainly because everybody working there is between 16 and 21, so it's always a right laugh. The free food is a benefit, too. It's also a job that is pretty much guaranteed... if you apply, you've essentially got it. If you refuse to work there on some kind of principal, then you have no right to complain about not being able to find a job (unless that principal is a dietry one, I could accept it if you were a diehard vegetarian, or something; except, that I'm a veggie and I can still cope 
).
As for your question. It's too risky. For one, increased votes might not mean increased seats. In the election, more people voted Conservative than voted for Labour in 2005 - which one resulted in the higher number of seats? Second, performing better in opinion polls doesn't always equate higher votes - Labour turned down the opportunity of an election in 2007 because they felt that the favourable opinion polls wouldn't translate over to votes. The opinion polls before the election also put Liberal Democrats ahead of Labour - yet the actual election was nothing like this.
You might say, well, they could still risk it, at worse they'd be in a similar situation, but, they won't. People would be pissed at them calling another election, which could mean more rebellion votes. Similarly, it's going to piss the Lib Dems off, meaning that coalition agreements would be harder, and they would demand more from it.
Conservatives would not gain from another election.
