Tony Blair said on Monday that the tens of thousands expected to protest in London against Bush over the Iraq war should recognise the country was better off without Saddam Hussein.
London will mount one of its biggest security operations ever during Bush's visit on 19 November as an expected 100,000 people cram London to berate him over Iraq.
"Protest if you will. That is your democratic right," Blair said at the Lord Mayor's banquet, a glittering London event that marks the prime minister's keynote foreign policy speech of the year.
Anti-war protestors say they will
flood London for the Bush visit
"Attack the decision to go to war, but have the integrity to realise that without it, those Iraqis now tasting freedom would still be under the lash of Saddam Hussein and his sons.
Blair, routinely lampooned by cartoonists as Bush's "poodle", denounced what he called a "poisonous propaganda monster" hounding America and feeding terrorism and extremism.
Blair, who was sweating profusely, looked uncomfortable as he delivered his speech. He has seen his trust ratings fall over his support for war in Iraq, especially among many in his own Labour Party.
"Attack the decision to go to war, but have the integrity to realise that without it, those Iraqis now tasting freedom would still be under the lash of Saddam Hussein and his sons"
British prime minsiter
"What is happening in Iraq? What is happening is that for the first time in 40 years, some semblance of broad-based government is being introduced," he said.
"Accept that the task now is not to argue about what has been, but to make what is happening now work, and work for the very Iraqis we all say we want to help," he said.
The war has put him at odds with the big continental European powers Germany and France, hurting his aim of acting as a bridge between the United States and Europe.
However, he said that the rift should be healed.
"If Europe were to let anti-Americanism define its foreign policy it would be a disaster for Europe, for Britain, for America," he said.
And Blair denied he was losing his grip on the delicate relations balancing act with the United States and Europe, the "two pillars" of British foreign policy.
"Both are in good shape and with a bit of vision and hard work, will be a more solid foundation than ever before."