Voters are disillusioned with the main parties

They should be concerned about the longer term implications of growing anti-European sentiment

On the basis of the poster voter (as opposed to the postal vote), the United Kingdom Independence Party will sweep the board on all roads leading out of London, through Surrey and West Sussex, all the way down to the south coast resorts of Bognor Regis, Littlehampton and Worthing.

On the basis of the poster voter (as opposed to the postal vote), the United Kingdom Independence Party will sweep the board on all roads leading out of London, through Surrey and West Sussex, all the way down to the south coast resorts of Bognor Regis, Littlehampton and Worthing.

Driving down to my parents' Sussex home on Sunday, the normal displays of Tory posters, which in the past usually vied with those of the Liberal Democrats, were this time curiously absent. Huge yellow and purple UKIP posters jump out at motorists from every strategic vantage point, proving that it is in the safe Tory heartlands where this new right-wing impostor appears to expect to make its greatest advance. Neither was there a single Labour poster in sight.

Of course, posters do not have votes, and one farmer's roadside fields, stretching for several miles and littered with UKIP signs, does not alter the fact that the poster erector only has one vote. It is clear, however, that the safer the Tory majority in parliamentary constituencies at the 2001 general election, the greater is the pool of potential UKIP votes.

But although, if the polls are correct, it is Michael Howard rather than Tony Blair who will be in the electoral dog-house when the ballots are counted next weekend, it would be wrong to suggest that, with one UKIP bound, the Prime Minister can breeze his way entirely safely to a third term victory. Much depends, of course, on the way in which the Tory party responds to the results. Their previous tendency to run around attacking each other, blame strategies, call for reshuffles and resort to their favourite pastime of backbiting, can certainly make an awkward situation worse.

Michael Portillo was right, however, to identify issuing the anti-UKIP briefing document as the Tories' single tactical error. This was compounded by Mr Howard dignifying UKIP with a speech that, in the words of Mr Portillo, "communicated nothing to the electorate except the smell of fear". Mr Howard should take a hard look at the undue influence that the co-chairman, Liam Fox, has had in this misguided strategy. This certainly turned out to be the catalyst for allowing the UKIP campaign to gain momentum in the final week. And, in turn, it has let the aggressive pro- and anti-Europe forces inside the Tory party escape from the bag into which they had been sealed when Mr Howard became leader.

But it is the Prime Minister and a Labour government that should be concerned about the longer term implications of growing anti-European sentiment. The real story of this election could be that a mere 50 per cent of voters in Thursday's poll will vote for either of the two main parties. The latest Populus poll suggests that the combined vote of UKIP, Greens and Liberal Democrats will equal the Tory and Labour votes. In the longer term, this poses just as awkward a threat to Labour, and sows the seeds for their disillusioned supporters to find new homes for their votes.

Immediately after the European votes are counted, the Prime Minister sets off for Brussels to conduct the final negotiations for the constitution. If he ignores the sentiment against the current drift of legislative power away from national parliaments to Brussels, he will find that the UKIP foothold on the political process will begin to threaten his own marginal constituencies.

So far, it has been assumed - probably correctly - that the UKIP advance has been at the Tories' expense. UKIP has merely capitalised on the soft "Eurosceptic" middle class vote. But if it subsequently manages to capitalise on the latent Europhobic vote among the council estates of Labour's traditional supporters, it could cost some marginal seats in the way the Referendum Party lost the Tories votes in the 1997 election.

This may not be enough to prevent a third term Labour victory, but there is a steady build-up of disillusionment against the political élites. We are pretty certain from Mr Blair's interview on yesterday's Today programme that the referendum on the new constitution will not come until after the next election. If Mr Blair does get safely back in office, it will then be his task to deliver a "yes" vote. And by having couched the whole debate on the basis that a "no" vote would, in effect, be a vote for withdrawal, he will continue to fuel the UKIP campaign in a way that even Mr Howard's unwitting strategists could not have dreamt of.

If some of Robert Kilroy-Silk's fellow candidates get elected on Thursday, although they may make little impact inside the European Parliament, they will be very much seen and heard in the months and years ahead - at least as much as the Liberal Democrats. They will also be given legitimacy by the Electoral Commission, which has to make a formal judgement on the rules over the funding and official representation of the "No" campaign. If Mr Howard wakes up to a headache next Monday when the election results are known, it will be as nothing compared to the nightmare to which Mr Blair may one day awake when the referendum result is eventually declared.

mrbrown@pimlico.freeserve.co.uk