Britain's military planners are drawing up contingency plans to send up to 1,700 extra troops to Iraq in response to the escalating violence.
Senior defence sources have told The Independent that lead elements could be flown out at very short notice if there were more bombings such as the ones that killed 68 people, including 17 children, in the south of the country on Wednesday.
Talks with the Americans over the reinforcements are said to be at an advanced stage. Any further deployment would not be concentrated purely in Basra, but outlying areas that have seen a spate of attacks on British troops. These are also on the routes through which insurgents from central Iraq are believed to be coming into the British-run sector to carry out attacks.
Senior Pentagon officials have told the Washington Post newspaper that Britain may provide a new headquarters unit to replace the 1,300 Spanish troops who are due to begin their withdrawal in the next 10 days. Following the Spanish decision, Honduras has said it will withdraw its complement of 370 soldiers, and the Dominican Republic its 300.
At present there are a total of 7,500 British service personnel in Iraq, with an additional 1,100 in surrounding countries. The plan had been to steadily reduce the numbers in the coming months.
President George Bush and Tony Blair have both endorsed a United Nations blueprint for the future of Iraq that could lead to other countries, such as India, Turkey, Pakistan and Indonesia contributing troops for Iraq.
United States and British commanders have warned that they expect a increase in violence in the run-up to the planned handover of political power to Iraqis after 30 June.
The US commander in Iraq, General John Abizaid, is expected to receive 10,000 extra troops, but, according to defence sources, British commanders are not keen on having any sizeable American presence in the British sector. There is widespread disquiet in senior ranks of the British military about the aggression of the Americans in civilian areas such as Fallujah.
Giving evidence before the Commons Defence Committee on Tuesday, General Sir Mike Jackson, the Chief of General Staff, took the highly unusual step of distancing British forces from the US tactics. "We must be able to fight with the Americans. That does not mean we must be able to fight as the Americans," he said. "That the British approach to post-conflict is doctrinally different to the US is a fact of life".
Tony Blair insisted yesterday that there were no immediate plans to reinforce British forces. But just a few hours earlier, Jack Straw, the Foreign Secretary, said: "The troop numbers are kept under review; the Prime Minister made this clear yesterday in the House of Commons. If there is a need for more troops to be sent, then I'm sure my colleague Geoff Hoon [the Secretary of State for Defence] will arrange for that to happen. I don't think there are political objections to send more troops if that is what is needed on the ground."
Nicholas Soames, the Conservative defence spokesman, said "We too have heard from very good sources that discussions are going on between the Americans and the British at a very high level about the sending of troops. The Prime Minister must be very ill-informed if he does not know this."
Sir Menzies Campbell, the Liberal Democrat spokesman on foreign affairs, said: "The US and British governments are caught between a rock and a hard place. To make progress towards the 30 June deadline, they need stability and security, but this is also the time we are expecting more violence. Even following a UN resolution, countries would want to deploy troops in a benign situation, not when there is mayhem going on."