Behind the move lies the erosion of President George W Bush's "coalition of the willing".
The Dutch started pulling their troops out after the Jan 30 Iraqi election on the basis that the advent of democracy meant that their mission was accomplished.
Last month the Queen's Dragoon Guards moved in to Muthanna province, 30,000 square miles of scrub and desert stretching from the Saudi Arabian border to the fringes of Basra and to just south of Najaf.
Last Tuesday the official handover was completed. Now only 200 of the 1,400 Dutch troops staged there for the past 20 months remain, and they will leave by the end of the month.
A force less than half the size of the deployment sent from Holland is now responsible for an area bigger than the two existing provinces already under British military authority - Basra and Maysan - put together.
But what struck the British troops as they took up their new posting was the lack of fanfare about what they were doing.
The handover ceremony was a muted affair barely mentioned in Britain. No British newspapers or television news crews were present, unlike in the January elections when 70 journalists were flown out at the Ministry of Defence's expense, or the scramble last November to deploy reporters with the Black Watch when it provided support for the American operation in Fallujah.
"It was a surprise," said Lt Col Tim Wilson, the commanding officer. "As this is Britain effectively taking over another province, and British soldiers doing a bloody good job."
His number two, Major Alan Richmond, had his view why: "With a general election coming [the Government] doesn't want reports of mission creep."
For mission creep it is. "Operational necessity", that military euphemism for plugging the dyke, means Britain has had to take on new responsibilities because no one else would do it.
Not that it is the most dangerous mission in Iraq. The opposite in fact. Although the British arrival was greeted by a rocket fired at the camp, Muthanna is considered one of the quietest provinces in Iraq. Not one Dutch soldier was killed or wounded.
Part of the reason is that few people live there. The southern area is home only to various nomadic tribes.
Samawah has a population of 215,000 people, the vast majority Shia, who wave at coalition convoys. Smuggling is the biggest problem.
Next month the 650-strong British contingent will be joined by 450 Australian soldiers tasked to provide security for a camp of 600 Japanese troops working on redevelopment projects.
The Japanese are under instructions by their government not to fire their weapons unless it is a matter of life or death, a position requiring other countries to provide them with protective support.
But responsibility for the province's security will be left with the British contingent. The intention is ultimately to hand over full control to the Iraqi army but no one can say when that will be, only that it will not be this year.
The soldiers freely admit they worry that replacing the Dutch could mark the start of a process in which the British are required to fill in the gaps as other nations leave.
Last week the Poles and Ukrainians announced their forces too are to be cut. Governments in Italy and Bulgaria are to vote this summer whether their troops should stay. Portugal quit in January. The Spanish left last year.
British manpower remains so stretched that even a deployment as small as the one to Samawah required 150 new troops being sent from outside Iraq to make up the numbers.
Brig Chris Deverell, in command of Basra's Fourth Armoured Brigade, said that if Britain was required to move in when other countries pulled out he would require more soldiers.
"If we are covering more of Iraq at the present threat level then we need more troops," he said. "Things are getting more benign and if that continues we may be able to extend the areas covered." But such a decision, he said, could only best be gauged in six months.
By Oliver Poole in Samawah (Filed: 14/03/2005)