By Nick Assinder BBC News Online political correspondent

If, as Tony Blair says, this is exactly the right time for George Bush to pay a state visit to Britain, it would be interesting to hear what the wrong time might be.

Blair is criticised for Bush support

When this visit was first being arranged in June last year, it may indeed have seemed like a good idea.

It would be the most potent symbol of the alliance between the two countries, and Tony Blair's extraordinary relationship with the Republican President and most powerful leader in the world.

The prime minister would have spun it as part of his ongoing vision of offering himself as an historic bridge between the US and Europe.

And he would have used it to present himself as a major figure on the world stage. He still will.

But this visit now looks much less straightforward for the prime minister. Although at least his rival party leaders have their own challenges.

End rows

When it was being planned months ago, few would have predicted just how seriously the situation in Iraq would develop.

Far from basking in a post-war surge in popularity, as many had predicted, the prime minister is facing continuing criticism of his decision to go to war in the first place and his actions since.

Bush faces anti-war protests

The war is widely seen as one of the major issues contributing to the loss of public trust in the government and the slide in the prime minister's popularity.

He is also facing repeated attacks from his own backbenchers, led by the likes of Glenda Jackson, Clare Short and, most dangerously, former foreign secretary Robin Cook who resigned his cabinet job in protest at the war.

It is understandable, therefore, that he is eager to move on and put the rows behind him.

Indeed in his annual foreign policy speech at the Guildhall a few days ago, he called for an end to the arguments over the war.

Symbolism

But the president's visit will ensure that all these arguments are re-ignited and given fresh impetus.

The anti-war movement is organising what many claim will be one of its largest demonstrations.

Protesters want to march through central London

And critics of Tony Blair's unwavering support for Mr Bush will be given more opportunities to voice their opposition.

Even the symbolism may backfire. The overwhelming US-led security arrangements risk adding to the impression that Britain is being forced to bow to White House demands.

Others have already suggested the president is using the visit to boost his own standing at home in the run up to next year's election.

So the outcome of all this is that, far from putting the controversies behind him, Tony Blair may well find they are given fresh impetus.

The other party leaders are presented with their own problems, however.

Liberal Democrat leader Charles Kennedy helped lead the anti-war sentiments in parliament.

He has now encouraged opponents of the war to get out on the streets and join the demonstrators while insisting it would be inappropriate for him, as party leader, to do so.

That is a tricky tightrope to walk and could leave him open to accusations of opportunism - even irresponsibility.

And new Tory leader Michael Howard will find it difficult to be too critical as he and his party supported the war and, supposedly, have a closer relationship with the Republicans than Labour do.