Labour may try to suppress it, but Iraq will still be the deciding issue of this election

Take Iraq out of the political equation and the Government would be sailing smoothly towards a third term

One issue tends to hover over election campaigns, not necessarily dominating the daily clashes between the parties, but always there in the background and much more significant than it seems. The hovering issue determines the tone, substance and outcome of the election.

One issue tends to hover over election campaigns, not necessarily dominating the daily clashes between the parties, but always there in the background and much more significant than it seems. The hovering issue determines the tone, substance and outcome of the election.

In the forthcoming campaign, the hovering issue is Tony Blair's decision to support the war in Iraq. At the moment, Downing Street insiders insist that Iraq is not an issue beyond a few middle-class London households. In the early hours of Friday 6 May, when the election result is known, I bet senior ministers will admit publicly Iraq was a big factor in determining the outcome.

In the 1997, election tax and public spending was the hovering issue. It barely featured in the daily news conferences, but that was because Labour had neutralised a previously vote-losing policy area by pledging to stick with the Conservatives' spending plans. This presented Labour's strategists with a problem: how to make the campaign exciting when they could not promise to invest very much? Very skilfully, they brought the campaign to life by gimmicks such as encouraging the journalist Martin Bell to stand as an anti-sleaze independent candidate.

The 1997 election campaign seemed to be about many issues, but really it was driven by tax, tax and tax: Labour could be trusted on tax; the Tories could no longer play the tax card. Tax was the issue that symbolised Labour's new credibility and the Conservatives' doomed cause.

In 2001 the hovering issue was the obvious unelectability of the Conservative Party. In the end nothing else mattered very much. There was not a great wave of enthusiasm for Labour, but it was clear the Conservatives had made no recovery since 1997. Their failure to do so had a wider symbolic message about the steady, incremental progress of the Government.

Iraq is already shaping the current campaign, at least in the way the national media is reporting it. Last week, when Tony Blair claimed the Conservatives would cut spending by £35bn, all hell was let loose. The popular press could hardly contain themselves and the populist wing of the BBC was foaming at the mouth with disapproval. After Mr Blair's over-the-top presentation of the intelligence on the non-existent weapons, his pre-election statements are being scrutinised much more sceptically.

This will not be wholly fair. He is running an election campaign, not a seminar. As election claims go, Mr Blair was not being outrageous in raising the prospect of cuts amounting to £35bn under the Conservatives. Over the next 10 years a Labour government would spend £35bn more than a Conservative administration. Political leaders often make such comparisons between future policies. Mr Blair was being much less contentious than his claim in the 1997 election that he could transform the NHS without a significant increase in public spending (in fact he was planning to invest more but could not say so because of the hovering issue of "tax").

But in 1997 Mr Blair walked on water as far as the newspapers were concerned. The broadcasters, taking their cue from the papers, gave him an easy time as well. Post-Iraq, if Mr Blair states that "Today is Thursday", his observation will be called to question.

Iraq has come to symbolise other questions relating to trust, the presentation of policy, and competence. Take Iraq out of the current political equation and the Government would be sailing smoothly towards a third term. Polls suggest that Labour is well ahead of the Conservatives on nearly all the key policy areas.

In spite of all the criticisms being made about Labour's approach to this election, it is still running a more mature and focused campaign than Howard and his party. This week Blair made a thoughtful speech on the modern role of the state in the provision of public services. As he delivered his words to church leaders, Mr Howard was visiting a Gypsy site.

There is no evidence to suggest that Labour voters are switching to the Conservatives. To some extent, they are more likely to return to Labour if they sense there is a real contest. But they may choose not to do so because of Iraq. This is what makes the election unpredictable. The unresolved question is the degree to which Labour voters will protest by staying at home or support the Liberal Democrats.

In crude political terms, the war against Iraq was a nightmarish trap for Mr Blair, as it would have been for any Labour Prime Minister. I wish he had been bold enough to break with the US over the issue, but the political risks of such a course were immense which is why it would have required an almost reckless but admirable political courage.

If he had opposed the conflict, Mr Blair would have lost the support of the Atlanticist wing in his New Labour coalition and almost certainly the endorsement of The Sun newspaper. By now columnists might have been writing that if only Mr Blair had supported the war against Iraq he would have been in a strong position to win the forthcoming election.

Instead, Mr Blair fell in to another trap. Seeking to purge his party's recent anti-American, "weak on defence" past and prove that a Labour Prime Minister could work closely with a Republican president, he has made his party more vulnerable. Future Labour leaders will seek to purge this part of their Blairite inheritance by showing they do not always dance to the tunes of a US president.

The war would have been so much easier for a Thatcher-style Conservative Prime Minister. Mrs Thatcher would have charged in with President Bush, the Mail would have cried "Rejoice", the BBC would have decided that whatever you think of her you must admire her courage as an international leader and that would have been the end of the matter.

For Mr Blair there will be no end to the matter. Iraq dominated yesterday's news agenda, with the Government responding to criticisms by Lord Butler of his informal prime ministerial style. Today the Defence Committee publishes a report that makes criticisms of inadequate military preparations. Nervy Labour MPs tell me that "Iraq" remains an issue on the doorstep. Voters praise much in the Government's record, and then raise the war.

These voters will have to decide what matters most to them, the substantial achievements of the Government on many domestic fronts or their disapproval of the war. A lot of them do not appear to have decided yet. Perhaps they will conclude that the Government's record matters more and, at the same time, in a dream scenario for him, Mr Blair wins some votes and newspaper endorsements precisely because of his support for the war.

It is possible that in a limited way "Iraq" works in his favour: angry progressives vote Labour in spite of the war and others support Mr Blair because of the conflict. Conversely, a large protest vote could wipe away Labour's landslide majority. This election is about Iraq, Iraq and Iraq.

s.richards@independent.co.uk