Almost ever since President Bush claimed an end to "major combat operations" in Iraq on 1 May 2003, debate has focused on how quickly troops could be withdrawn.

The US and British governments say troops will remain in Iraq "until the job is done".

Yet while the withdrawal of a substantial number of troops remains an aim, it has become increasingly clear that the Pentagon and the British Ministry of Defence (MoD) are preparing to retain some forces in Iraq for the longer term. The US currently has around 130,000 troops in Iraq; Britain has 8,000.

Major Joseph Breasseale, a senior spokesman for the coalition forces' headquarters in Iraq, said: "The current plan is to reduce the coalition footprint into six consolidation bases . . . four of which are US. As we move in that direction, some other bases will have to grow to facilitate the closure [or] transfer of smaller bases." He added: "Right now, I don't have any information that tells me which nationality will comprise the remaining two bases, though my assumption is that at least one will be run by the Brits."

A British Ministry of Defence spokesperson said British forces were currently operating out of eight bases in southern Iraq, with a small contingent based in Baghdad, and that "discussions with coalition forces relating to future basing are still at a very early stage. Nothing has been agreed."

The official added: "We have no intention of remaining, or indeed retaining bases in Iraq long-term. We will leave Iraq as soon as the democratically elected Iraqi government is confident that its security forces have the capability and capacity to counter terrorism and to preserve the security of democracy there."

A senior military source recently said that some British troops could be expected to stay in Iraq in a training role for years to come. There would be no British presence in the urban areas, however. The American and British governments say they remain in Iraq at the invitation of the interim Iraqi government, and would leave if asked to do so. Such a request could come if the radical Shia bloc, which won most seats in December's election, refuses to form a government of national unity with Sunni and secular Shia politicians.

The Pentagon says it has already reduced the number of US bases from 110 a year ago to a current total of around 75. But at the same time it is expanding a number of vast, highly-defended bases, some in the desert away from large population areas. More than $280m has already been spent on building up Al Asad air base, Balad air base, Camp Taji and Tallil air base, and the Bush administration has this year requested another $175m to enlarge them.

These bases, which currently house more than 55,000 troops, have their own bus routes, pizza restaurants and supermarkets. The base at Balad, north-east of Baghdad, measures four-and-a-half miles by three miles.

Some analysts believe the desire to establish a long-term US military presence in Iraq was always one of the reasons behind the 2003 invasion. At the time, Paul Wolfowitz, the deputy US defence secretary admitted the purported threat of 'weapons of mass destruction' had been selected as a reason to invade Iraq "for bureaucratic reasons". He added: "There are a lot of things that are different now, and one that has gone by almost unnoticed . . . but it's huge . . . is thatf we can now remove almost all of our forces from Saudi Arabia."

Welsh MP Adam Price, a constant critic of the Iraq war, said it would be "very, very worrying" if British troops were to be involved in a longterm deployment. "Certainly the mood music has all been about the withdrawal of troops, " he said. "Now we are just starting to see the glimmers of what may be the real policy."

Joseph Gerson, a historian of American military bases and director of the peace and economic security programme at the American Friends Service Committee, said: "The Bush administration's intention is to have a long-term military presence in the regionf For a number of years, the US has sought to use a number of means to make sure it dominates in the Middle East. . . The Bush administration sees Iraq as an unsinkable aircraft carrier for its troops and bases for years to come."

Zoltan Grossman, a geographer at Evergreen State College in Washington, said:

"After every US military intervention since 1990 the Pentagon has left behind clusters of new bases in areas where it never before had a foothold.

The new string of bases stretch from Kosovo and adjacent Balkan states, to Iraq and other Persian Gulf states, into Afghanistan and other central Asian statesf The only two obstacles to a geographically contiguous US sphere of influence are Iran and Syria."

The US and UK repeatedly say the timetable is dependent upon success in training Iraqi forces. Progress in this area has been slow; in February the Pentagon admitted the only Iraqi battalion judged capable of fighting without US support had been downgraded, requiring it to fight with American troops.