The son of Rose Gentle (right) died in Iraq in June last year

The 11-member delegation, from the newly-formed Military Families Against the War, included Rose Gentle and Reg Keys, who both lost sons in Iraq.

Earlier on Wednesday, Number 10 officials said there was "nowhere formally to lay a wreath".

However, the relatives were eventually allowed to place it on the doorstep.

There had also been doubts about the delegation's plans to hold a minute's silence, but that was permitted before two of them entered Number 10.

'Responsibility'

The pair delivered a letter from the anti-war movement, as well as photos of their children, Black Watch headgear and the wreath.

The letter accused Mr Blair of "morally unacceptable conduct".

After the visit, Mr Keys said: "We're not anti-army, we're not left-wing radicalists, we just want our boys back home safe.

"We want Tony Blair to realise that the responsiblity for the death of these men lies on his doorstep."

He said the parents realised that their children may face danger when they sign up for the Army, "but not for lies and not for deceit about WMD".

The boys want to come home and I don't mean just for Christmas Rose Gentle More UK casualties in Iraq

He added that the oath of allegiance worked both ways: "Surely the government owes the lads that sign up some loyalty, some integrity."

The action follows the recent deaths of four UK soldiers in Iraq, after a series of attacks targeted Black Watch troops based at Camp Dogwood, 20 miles (32km) south of Baghdad.

The bodies of three of the soldiers, killed in a suicide bomb attack last Thursday, were due to arrive back in the UK on Wednesday.

The wreath was to symbolise Tony Blair's "culpability" said Mr Keys, 52, from Llanuwchllyn, in north Wales.

'Tony Blair's doorstep'

The wreath, carried by representatives of six families, would represent the British personnel killed and would "also symbolise that the blood of these men lies on Tony Blair's doorstep", he said.

The prime minister's official spokesman had earlier said: "If they wish to bring a wreath to Downing Street and give it in through the door that's fine by us. "

A total of 74 UK service personnel have been killed in Iraq since the conflict began last March.

Mr Keys' son, L/Cpl Thomas Keys, was one of six Royal Military Police killed by a mob near Basra in June last year.

Thomas Keys, 20, was killed by a mob in Basra

Ms Gentle, from Glasgow, lost her son Gordon, 19, while he was serving with the Royal Highland Fusiliers in Basra in June.

"One woman phoned me last night saying she had spoken to her son over there and he'd told her: 'Ask Mrs Gentle to keep the campaign going'," she said.

"The boys want to come home and I don't mean just for Christmas.

"Tony Blair must pull the troops out so Iraq can get back to their own way of living, they've got their own government now and they don't want us there."

The campaign group will also to hold a private meeting on Wednesday with more than 50 MPs from all parties, followed by a vigil and rally at Parliament Square.

The 850-strong battle group, re-deployed on 27 October from Basra in southern Iraq, moved into the US-controlled zone to allow US Marines to prepare for their assault on Falluja.