"The defences have been weakening so the forward battlegroup commander and the brigade commander, as entirely in line with the way we operate, made the decision this morning, here's the opportunity, the conditions are right, let's go for it," Vernon told Sky News.

"Constantly we've been eroding on the outskirts.

"We've been targeting the Baath party officials and the irregulars very, very successfully and we had a very big hit the other day on some very senior officials," he said.

The British so-called Desert Rats, from the 7th Armoured Brigade, met "patchy" resistance as the troops moved in from the south west, an unnamed military source told the Press Association, Britain's domestic news agency.

The source, at Central Command in Qatar, said there was some "stiff fighting" early Sunday morning.

In London, a spokeswoman for the British defence ministry declined to comment on the reports.

But she said that the war was not a conventional conflict with a front line, and that units could enter the city and withdraw as they please.

A reporter with Britain's ITV News, Juliet Bremner, who was with the rolling convoy heading into the centre of Iraq's second city, said hundreds of tanks were travelling down one of the main highways which leads directly into the north of the city.

"As far as we know there shouldn't be too much of a problem getting into Basra itself. There seems to be nothing to stop them," she said.

"No rocket propelled grenades have been fired at the convoy so it should be a pretty straight-forward route into the city. There are no signs of firing or any signs of resistance," she added.

SPACE.WIRE