Ten reasons why Blair can't afford to relax

Neither side believes the the size of Blair's lead. The fight is not over until 10pm on 1 May

It's been Labour's week again. First, The Sun transforms the landscape by backing Tony Blair. Then the Tories are put hugely on the defensive over cash for parliamentary questions - overshadowing one of the best ever monthly falls in unemployment. In hand-to-hand fighting for the headlines the Tories have already suffered heavy losses, and the campaign has scarcely begun.

So it seems eccentric to suggest that Labour, around 20 points ahead in the polls, has any reasons for anxiety. If anything its support seems to be hardening. But that's just it. Both parties are deeply suspicious of the size of the poll lead and, ironically, both would probably like them to narrow to what Labour regards as a real gap closer to 10 per cent. The Tories, so that they can improve morale and promise the kind of real fight that the electorate and press would like; Labour so that it would inject a more realistic view of the work that still needs to be done. Complacency is Labour's big enemy. So for hubristic Labour candidates and party workers here are 10 potential problems to worry about:

1. The reverse incumbency factor. The bright lights are now on Labour. Because of the widespread assumption that Blair will win, significantly more interest is being shown in Labour's policy proposals by the media, and by the Tories themselves, now effectively fighting the election as an opposition party. Earlier this week the Evening Standard put 50 questions about Labour's programme to the party. When asked why the same proposals were not being put to the Tories, the reply came back: "because no one thinks they're going to win."

2. Money. John Major's biographer, the historian Anthony Seldon, has listed nine factors for why Tory governments fall - ranging from party disunity and a negative image of the leader to feeling that it is time for a change. Major's government displays eight out of the nine. The one it doesn't is money. Tories won't say how much they have got but Labour puts the figure at pounds 40m compared to pounds 12m of its own. This means much more for newspaper advertising, direct mail shots and telephone canvassing.

3. TV debates. Labour strategists are quietly confident that debates will work to Blair's advantage, but several senior Tories believe they will help Major. And as the first in British political history they cannot fail to inject an whiff of danger into an otherwise heavily programmed campaign. At present both the BBC (front man: David Dimbleby) and ITV (Jonathan Dimbleby) are proposing two 90-minute Sunday night debates, with an expected audience of 15 million, in mid-campaign. Blair and Major would confront each other, with Ashdown being grilled separately. ITV envisages a looser, more audience friendly format with more cross-talk between the two main leaders. BBC would have Ashdown on at the end, ITV in the middle. The main obstacle is Ashdown's understandable reluctance to be left out of the main debate. But the balance is tipping in favour of debates. That means danger for both sides, and Major has less to lose.

4. Europe: The shuffle by the Cabinet in January when it agreed that a single currency was "highly unlikely", followed by an amber light to candidates opposing the single currency outright has meant that many Tory candidates are running their own campaigns without reference to Central Office, and not just on Europe. If the sceptics are even half right about their popularity, some Tory defectors might be won back.

5. Immigration. First it seemed as if Major was slapping down any attempt by Nick Budgen and his fellow right-wingers to exploit the difference between Tories and Labour on the primary purpose rule covering spouses of immigrants. Now it seems there won't be a full scale press conference on immigration. But MPs like Budgen will be free to campaign on the issue and Michael Howard will almost certainly mention it. This is undermining Tory support among Asian voters. But it could still be a negative for Labour among wavering white C2s.

6 Potential Sun backlash. Murdoch's swing to Labour makes it unlikely the Daily Mail will follow suit. This is partly for reasons of competition and partly because of the old adage that the best commercial position for newspapers is to be Tory at times of a Labour government. The main danger among activists is a feeling that now The Sun has switched sides the battle is over bar the shouting. This is a big mistake. It wasn't the Sun wot won it in 1992. It had much more to do with Labour's tax plans and Neil Kinnock's unpopularity. Michael Heseltine is straining at the leash to deliver a broadside at foreign newspaper tycoons, but Central Office is much more reluctant, possibly because huge efforts were made by senior ministers to stop Murdoch doing it. The overall effect is a big net gain. But Labour may still play a price, especially among the chattering classes, Conservative defectors who dislike The Sun, and rival newspaper groups.

7. The landslide factor - the risk of a counter-swing against Labour once electors start seriously translating the poll lead into a 1906-style majority. As the Tories point out, Labour's planned constitutional changes are for ever - and not just until the next Tory government takes over. One way of preventing this is by stamping on the related problem of ...

8. Triumphalist indiscipline. All senior Labour spokesmen need an urgent inoculation against Sheffield syndrome - the ailment which caused Neil Kinnock to lose it at the pre-election rally in 1992. This is one reason why Blair is campaigning in meetings with small groups of voters rather than tub-thumping US-style presidential rallies. Shadow ministers with eyes on Cabinet jobs are particularly susceptible .

9. It's the economy, stupid. It's true that the Tories are suffering from an unprecedented disjunction between economic optimism and their own popularity. But the 1p tax reduction due in April certainly won't harm the the Tories.

10. The Max Clifford factor. The effect would probably be limited. But just because The Sun has swung to Labour it can't be ruled out that Labour, as well as the Tories, could be hit by prurient sexual revelations before polling day.

The two men most aware that it could yet be a much tougher fight are Blair and Major. Blair starkly warned his MPs this week that "we have a mountain to climb" and that just to get a majority Labour needs its biggest swing since 1945. This doesn't mean that a landslide isn't possible. Even a 10 per cent lead would deliver an awe-inspiring 80-seat majority. But it does mean that Labour would be wise to treat the mysterious electoral beast with deep respect all the way to 10pm on Thursday May 1.