Tens of thousands of Britons are planning to flood into the UK capital to protest over Blair's support and commitment to America over occupied Iraq.
American and British military occupation and continued Israeli aggression will be the focus of the speakers at the rally on Saturday.
Demonstration organiser John Rees said he predicted 100,000 would turn up to condemn “US plans to dominate and reshape the region, rather than bring peace, security or democracy – as was the claim prior to the outbreak of war.”
The Campaign for Nuclear Disarmament, Stop the War Coalition and the Muslim Association of Britain (MAB) all plan to march from London’s Hyde Park to Trafalgar Square on 27 September.
Rees added that MPs billed to speak at the demonstration may include one-time Blair ally and former minister Robin Cook whose resignation speech over Iraq shook the British prime minister.
Labour stalwarts George Galloway MP and retired MP Tony Benn are also expected to speak at the rally.
MAB spokeswoman, Yasmin Ata Allah, said Blair’s claimed the war on Iraq would open the way for a just peace in the Middle East and the establishment of a viable and sovereign Palestinian state now seemed "utterly absurd".
“In fact, the government has recently sanctioned policies that subject the Palestinians to further injustice and oppression and offers support to the Israeli side, despite the internationally recognised brutal and inhumane occupation it imposes.”
Blair feeling the pressure
The demonstration follows a terrible by-election result for the Labour party, when a ‘safe’ majority of 7040 votes was overturned in the formerly rock-solid parliamentary seat of Brent East.
Despite a large majority, Blair's
days as leader look bleak
The protest also comes after a failed weekend summit of Europe's three big powers.
The consensus among commentators was that the talks on Saturday in the German capital had merely exposed the faultlines over policy towards Iraq again.
Britain’s Sunday Times newspaper said Blair, for whom the summit was seen as a chance to reconnect with his European partners, had returned "empty-handed."
Former Labour party minister Frank Field said he saw the prospect of losing the next general election on a record low turn-out increasingly likely and added “we are in deep trouble”.
Describing the by-election defeat as “very disappointing”, Labour chairman Ian McCartney blamed media coverage of the Iraq war and the Hutton inquiry - which questioned dodgy British intelligence used to justify the invasion.
Blair ally Stephen Byers put the defeat down to arrogance. “We’ve been so successful at the polls that we just take it as a given that we’re going to win. That isn’t the case.”
But a Blair official spokesman said people would appreciate the Government’s policies over time. “In any programme of change it always takes time to see the results at street level.”