Almost all of the UK's 4,100 troops will leave Iraq by July 2009
The head of the British army has said UK troops in Iraq may have to "pause for a day or two" while their legal status is confirmed.
Sir Richard Dannatt was speaking after Iraqi MPs postponed a vote which would allow non-US forces to remain in the country after the end of the year.
He said "arrangements were in place" to allow UK forces to operate, whether the Iraqis passed the legislation or not.
About 4,000 British troops are helping to train and mentor Iraqi forces.
The delay to the Iraqi parliament vote means that non-US troops will have no legal basis to stay in Iraq after the current UN mandate runs out on 31 December.
In an interview with the BBC, Sir Richard declined to elaborate on what the "arrangements" were that would allow UK troops to operate without a legal mandate.
But he did concede that training and mentoring operations in the southern Iraqi city of Basra may have to go on hold for a short time.
Iraqi MPs are not scheduled to reconvene until 7 January 2009, although an extraordinary parliamentary session may be held before then.
Some Iraqi lawmakers are now calling for a special session on Tuesday afternoon on which they could vote on the resolution.
The US has already struck a separate security pact to keep troops in Iraq to 2011.
Sir Richard said he "completely refuted" critics who said British forces stood aside while Iraqi and American troops took on militias in Basra last spring.
He said some commentators were rewriting history, and that Basra was always going to be sorted out by the Iraqis.
He added that the size of Basra meant that it would have been impossible for British forces to impose a regime, something they had no intention of doing.
Sir Richard said the UK "struck no deal" with militants to allow British forces to withdraw from the city centre, but merely "created some space" for Iraqis to solve their own problems.
He said Basra had now been transformed.
'Not in vain'
Meanwhile, responding to an article by former Conservative defence secretary Michael Portillo in the Sunday Times, Gen Dannatt said he was "dismayed" by some recent criticism.
Mr Portillo had said the UK has "failed" to provide security for the Iraqi people, and that the decision to withdraw UK troops in Basra to their barracks had been "shaming".
Sir Richard said: "I wonder at the wisdom of armchair critics who have sat very comfortably at home while soldiers, sailors, airmen and marines have fought with extreme valour over the past six years."
He added: "This was always about regime change, a very difficult political undertaking."
He said he wanted to assure the families of the 178 personnel whose lives have been lost that their loss had not been in vain.
Gen Dannatt would not be drawn on how long it would be before significant additional troops would be sent to Afghanistan.
He said he was "absolutely clear" that he was not going to allow the pressure the army had been under in recent years to be replicated over the next several years.