A series of protests around the country culminated in the clashes in London which saw five police officers injured and eight demonstrators arrested.
Political opposition to the Prime Minister was also gathering momentum with outspoken Labour backbenchers George Galloway and Tom Dalyell gaining cross-party backing from the former Tory prime minister Sir Edward Heath.
Last night Mr Galloway's attempts to hand in a letter of protest at Downing Street ended in a scuffle when three of his delegation who had been allowed through the security cordon to No 10 attempted to barge their way into the building and chain themselves to railings. Police grappled with the men and wrestled them to the ground as Mr Galloway posed in front of Mr Blair's brightly lit Christmas tree on the doorstep.
As they were handcuffed by police, Mr Galloway and the prominent Arab lawyer Sabah Al-Mukhtar were escorted out into Whitehall.
Armed police were on stand-by, but were not needed as local policemen who had escorted the party into the street, took immediate command of the situation.
Mr Blair had made a statement from No 10 less than an hour before the incident, and was still in the building.
Mr Galloway, Labour MP for Glasgow Kelvin, has outraged Mr Blair and fellow MPs by his public criticism of the bombing of Iraq.
The three men held by police were taken to Charing Cross police station for questioning. The men, all British, had been wearing brightly-coloured anoraks and one had a red and white Arab-style scarf.
After the arrests, Mr Galloway crossed Whitehall and addressed a crowd of about 250 demonstrators. Over a public address system, he chanted: "Are you listening, Tony Blair?"
Police Superintendent David Commins said: "Mr Galloway asked me if he could deliver a letter to No 10, which I was happy to let him do. I asked him if he could vouch for the others in his party and he said he could.
"The three men have been taken to Charing Cross police station for questioning."
The men were searched in Downing Street and found to have handcuffs on them.
Mr Galloway said later: "I do not know what these people did. These are very emotional times, especially for young people." Mr Galloway said he had allowed the three men, all of whom were British, into Downing Street with him because they had asked him if they could go.
Earlier, violent scenes broke out in Whitehall as police tried to arrest Muslim protesters who burned an American flag.
Five policemen were injured as they clashed with about 30 protesters. One officer had a large bruise and cut to the side of his face and another was kicked in the head.
Some demonstrators shouted they would kill the officers while others threw bottles and sticks. Five people were arrested and were being questioned last night.
Other protesters returned behind barricades erected by police and dispersed after facing Mecca and praying.
Later, a Scotland Yard spokeswoman said that the officers were examined by a medical officer and did not need hospital treatment.
One had facial injuries, another a minor head injury and a third was hit on the arm by a bottle.
Two protesters were arrested for assault, two more for public order offences and one for possessing an offensive weapon.
A Scotland Yard spokeswoman said later: "Three men attempted to handcuff themselves to the railings outside the front door.
"Police officers acted very quickly and prevented this from happening. Three men were arrested for public order offences."
Sir Edward Heath lent his support by joining Labour dissidents in condemning the bombing of Iraq as "dubious" and criticised Tony Blair for giving unequivocal support to President Bill Clinton for the offensive.
The Christmas recess of Parliament robbed the rebels of any chance to mobilise their forces at Westminster against the bombing, but they claimed that more Labour MPs would be under pressure from their constituency parties to come out against the attacks this weekend.
Sir Edward's intervention, on BBC radio, is likely to make Labour MPs more uncomfortable. Sir Edward criticised the British and American leaders for failing to set out clear objectives for the use of force, and made it clear that he was against giving the US uncritical support.
"I believe we should always keep separate on these things. The whole setting of this enterprise has been so dubious, especially when the President of the United States has got his own domestic problems. We are going to see them going on together," he said.
Sir Edward, who met President Saddam Hussein during the 1991 Gulf crisis while on a mission to seek the release of hostages, said the aims had not been clearly defined.
"How long are they going to keep on? They don't even know whether they are going to go on through Ramadan. Are they aiming at dethroning Saddam Hussein - if so, what happens if they don't? All these are open questions."
Left-wing Labour opponents of the bombing in Iraq were still seething about the whips' ploy which stopped them voting against the Government on Thursday night following a Commons debate.
Tam Dalyell, Labour MP for Linlithgow, said the refusal to put tellers on for a late-night vote, to avoid a division, in the Commons, had infuriated Labour MPs who had wanted to register a protest against the Government.
"I don't think matters of peace and war are matters for parliamentary games or wheezes," he said.Reuse content