By Nick Assinder BBC News Online political correspondent

Blair has decided to take on his war critics

For the past number of months, and for very good reason, Tony Blair has been trying to shut down the row over Iraq with pleas for his critics to put it behind them.

It has failed and the prime minister knows it. He has now decided the only option he has left is to meet his detractors with his fists up.

And that is precisely what he did in his performance in his Sedgefield constituency.

Stemming the flow?

His robust speech may even mean the rows continue as his critics challenge the content of his speech and answer the stinging attacks on them as "naive or derelict".

But the prime minister must have calculated that is preferable to the corrosive, drip, drip which has see the issue dogging him since the end of the conflict and blown his domestic agenda off course.

In terms of content or policy, his speech had little new to offer. He repeated his insistence that his critics were really questioning his judgement rather than his trustworthiness.

The question now is whether this will do the trick and finally start turning the tide

He again said he went to war to enforce the demands of the UN, suggesting that body had failed or been unable to meet its responsibilities and needed significant reform.

And he said he had never suggested the threat to the UK from Saddam Hussein had been "imminent" or that he had given undue prominence to the claim Saddam could have launched WMD attacks within 45 minutes.

He even rehearsed many of the issues that had gone before Lord Hutton's controversial inquiry.

'Frightening' prospects

But by far the most powerful part of his speech - the bit he wanted to drive home - concerned the scale and reality of the threat posed to the world and Britain by international terrorism and rogue states.

In some of his strongest language yet on the threat, he painted a genuinely frightening picture of terrorists seeking weapons of mass destruction to bring down Armageddon on the world.

He clearly wanted his message to shake people, but he also wanted to avoid claims he was engaging in scare tactics

Preventing that horror was one of the main reasons he went to war on Saddam Hussein when the UN hesitated, he said.

It was a difficult line to walk. He clearly wanted his message to shake people, but he also wanted to avoid claims he was engaging in scare tactics designed to shift the argument.

He also wanted to underline his argument that the decision to go to war had been a matter of judgement.

He could have acted differently, or not acted at all. But as the country's leader he was compelled to make a judgement.

And he was setting out as clearly as he possibly could the reasons behind the judgement he eventually took.

Shifting opinion

The question now is whether this will do the trick and finally start turning the tide over what he confessed was the most divisive decision he has ever taken.

Some believe it may already be too late, that voters have already made up their minds about how and why Britain was taken to war.

If that is true, then it is probably bad news for the prime minister.

If there is still room to shift opinion before the next election, this was as good an attempt as any to start that process.