The Iraqi general studies a map with a British officer at a border control post metres from the coastal point in southern Iraq where hundreds of British Marines stormed ashore at the start of the war five years ago.

The two commanders, once on opposing sides, now discuss plans for a joint raid against smugglers of weapons, cars, oil and even sheep, as part of a limited British effort to build up Iraqi security forces.

The harmonious scene is in stark contrast to the situation up the road in Iraq's second city of Basra, where Iraqi police and soldiers operate alone. British forces are no longer welcome, having handed over control of security and pulled back to their airport base.

The near-daily thump of rocket fire on the camp serves as a constant reminder of the problems here, despite British commanders' insistence that violence is in decline and the Iraqis are able to manage on their own.

The Marines who pushed up through al-Faw Peninsula, right past the border control post on the night of March 20, 2003, to secure Iraq's oil infrastructure could never have predicted that five years later the British military would still be here. The people of Basra have also readjusted expectations. While applauding the end of Saddam Hussein, many are unhappy with the rise of rival Shia militias and the inability of their new political leaders to provide security.

In addition, unemployment is high and, while the availability of electricity and water has improved, there is still a long way to go. Also, Iraq's multibillion-pound oil resources remain largely untapped — foreign oil giants are too fearful of the violence to venture into the country and invest.

The insecurity has cast serious doubts over plans to reduce Britain's military presence in Iraq to 2,500 troops by the spring. Next week Des Browne, the Defence Secretary, will announce that another full brigade will be sent to Basra in May to replace the existing 4,100 troops.

There had been expectations that a smaller force would be sent for the next troop rotation. The Desert Rats — 7th Armoured Brigade — will now deploy in May and June for a six-month tour.

One battlegroup of about 500 soldiers in Basra had been told that it might be sent home two months early, but is now committed to serving a full six-month tour until June.

Lieutenant-Colonel Gary Deakin, commanding officer of the Duke of Lancaster's battle group, said: “What was clear right from the word go was that it would depend on the situation.”

The British military, which was responsible for Iraq's four southern provinces after the invasion, has cut its presence over the past year while the US has deployed an extra 30,000 troops into Baghdad and the surrounding belts to tackle violence there.

Deeming the Iraqi Army, police and local political leaders to be ready, Britain has also gradually handed control of security to the Iraqis in Muthanna, Dhiqar, Maysan and finally Basra, a symbolic shift that took place in December.

British troops are now given the task largely of trying to protect themselves at the airport as well as continuing to train Iraq's police, military and border and coastal guards. There are concerns, however, about the continuing effectiveness of such a mission if troop numbers dwindle further.

“I think the key challenge is at what force levels do you achieve what you need to achieve to make your ship sail forwards or just keep it sitting in the water,” said Colonel Deakin, who on Tuesday was planning the counter-smuggling operation with Brigadier-General Abdul Hade, operational planner for guarding Iraq's wet border.

He added: “Right now the ship is going forwards. We are rowing forwards in the right direction. If you take out a couple of oarsmen maybe the tide would flow against you.”

Throwing pressure on Gordon Brown to resist further troop cuts, Hoshiyar Zebari, the Iraqi Foreign Minister, this week accused the military of doing nothing.

“The militia, the organised crime, is making havoc in the city,” he told Channel 4. Asked if Britain needed to re-engage rather than pull troops out, he said: “In my view they do.”

The majority of Britain's forces are holed up at the airport base, where nerves are frayed by the constant threat of rockets, although the number of attacks is vastly reduced from its peak last summer. The 175th British personnel to die since 2003 was killed by a rocket two weeks ago.

Many soldiers say that they would rather be involved in the more hands-on action that British troops are experiencing in southern Afghanistan.

“I have already got the medal for here. I would rather be doing an infantry job out there,” said Lance Bombadier Ben James, 23.

The calculation that any movement by British forces inside Basra city would create a violent militia backlash means that no troops have been in the city since September. This also prevents officials from the Foreign and Commonwealth Office and the Department for International Development from getting out and seeing first-hand the impact of reconstruction efforts.

John Moss, head of programmes for Basra's provincial reconstruction team, said: “As long as southern Iraq remains off limits to non-Iraqis then it's going to be extremely difficult for them to grow their economy.”

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