Professor Colin Mellors: In this tight poll battle, there may be more surprises ahead

While voters are rejecting Labour, the Conservatives cannot find the support needed to win outright. And, even with his current popularity, Mr Clegg at best becomes king-maker rather than heir apparent to Number 10. The surge that followed the first television debate is largely holding and, two weeks on, there is only a slight slippage in the Liberal Democrat share which still averages 29 per cent. New converts are more likely to be young than old, female than male, and middle class than working class.

Modest Conservative improvement can be detected, but the party remains short of the 10-point lead over Labour needed to be confident of an overall majority. Only two polls in the last seven days give them more than 35 per cent.

The small comfort for Labour is that things have not worsened and, while they still trail in third place in most polls, the latest indicate they might just be closing on the Lib Dems. Overall, however, their campaign appears to be consolidating their core vote rather than attracting undecided electors.

Some of the most intriguing figures come from the PoliticsHome/YouGov calculation of regional voting intentions which indicates significant variations across the country. These suggest the possibility of nine Conservative losses to Liberal Democrats in the South West, but even more Labour losses to the Lib Dems in the North, where the swing to Lib Dem (over 10 per cent) is approximately twice that in the South.

If accurate, it could mean Liberal Democrats taking relatively safe Labour seats in urban areas, building on the party's recent council election successes. According to regional patterns, Conservatives would benefit nationally by up to 20 seats – still short of an overall majority but overtaking Labour as the largest party.

The differences between national and regional polling data are shown in the chart. In Yorkshire, the latter doubles the number of vulnerable Labour seats.

With one more television debate and seven days of campaigning remaining, there is still time for all this to change.

For Liberal Democrats, the challenge is to ensure that votes do not drift away; Labour's is to persuade that, in difficult times, "substance and experience" outweighs everything else; and the Conservatives' that it really is time for fresh ideas.

Finally, there is the polling industry "small print". In normal circumstances a potential three per cent margin for error is of little consequence. With this race so tight, it could conceal the difference between an indecisive outcome and outright victory. There may still be some surprises in store.

Professor Colin Mellors is a political scientist at the University of York.