Anti-war protesters claim that US authorities have demanded a rolling "exclusion zone" around President George Bush during his visit, as well as a ban on marches in parts of central London.
The Stop The War Coalition said yesterday that it had been told by the police that it would not be allowed to demonstrate in Parliament Square and Whitehall next Thursday - a ban it said it was determined to resist. The coalition says that it has also been told by British officials that American officials want a distance kept between Mr Bush and protesters, for security reasons and to prevent their appearance in the same television shots.
The Metropolitan Police banned the Parliament Square and Whitehall route by the use of Sessional Orders - which can be enforced for such a purpose when Parliament is in session.
MPs supporting the protests saydemonstrations have been allowed while Parliament was sitting, and, in any case, it was unlikely it will be doing so on the day of the proposed march.
The mayor of London, Ken Livingstone, said yesterday that Mr Bush should not be shielded from public anger about the Iraq war, and Londoners should not have to pick up the £4m policing bill. He said: "To create a situation in which perhaps 60,000 people remain unseen would require a shutdown of central London which is just not acceptable."
It is reported that Mr Bush's entourage will number around 500 with up to 200 members of the security service. The Americans are also said to be bringing a US Marine Corps Sea King helicopter, a Black Hawk helicopter and 15 sniffer dogs.
Organisers say they expect between 50,000 and 70,000 people for the biggest protest against a visiting head of state. Andrew Burgin, of the Anti-War Coalition, said: "We have refused to sign off the agreement over Parliament Square and Whitehall, and we shall certainly also refuse to do so on this whole idea of an exclusion zone." He said: "If there is no agreement by next week, we have a potentially highly risky situation with so many protesters in the centre of London."
Jeremy Corbyn, the Labour MP, said: "[The police] are under pressure from the Americans, and the losers appear to be people of Britain who want to show their opposition to the Iraq war."