Gordon Brown is considering rejecting an expected request from Barack Obama, the US President-elect, to send 2,000 more British troops to Afghanistan to join the surge of US forces confronting the Taleban.

Britain is expected to come under considerable pressure from Mr Obama when he becomes President in January to send another battle group of 1,500-2,000. Turning down such a request would open a rift between Britain and the US. British military chiefs have also been clamouring for reinforcements for the beleaguered troops in the southern Afghan province of Helmand.

Senior military officers have begun drawing up plans for boosting the British presence in southern Afghanistan to more than 10,000. Secret planning has been under way for some time to deploy another 2,000 troops, although the Ministry of Defence has previously denied reports that reinforcements were likely to be sent next year.

British officials fear that if Britain fails to send more troops, the US will take military control of Helmand and sideline the British. Under US surge plans to send 20,000 more soldiers next year, the Pentagon is planning to deploy 5,000 into Helmand to join the British effort, and a further 5,000 into neighbouring southern provinces.

The British military, however, has made it clear that it is overstretched. “We're at the maximum of what Britain can do in the world,” one source said. Mr Brown, who spent Saturday in Afghanistan reviewing the state of the conflict, is being urged by advisers not to expand the force beyond the 8,400 troops now in place in Helmand province and in neighbouring Kandahar at a major airbase.

Mr Brown was given a bleak assessment of progress in the fight against the Taleban. He was told that there were still daily attacks at Musa Qala, in northern Helmand, which British and Afghan troops seized back from the Taleban. The rate of suicide bombings also remains high.

According to sources the Prime Minister is concerned about the potential cost of the extra deployment when government finances are so tight. Funding for the operation in Afghanistan has to come out of Treasury reserves. Mr Brown is also thought to be worried that public opinion might turn more strongly against the campaign if the number of casualties continues to rise.

Despite Mr Brown's apparent doubts about sending another 2,000 troops to Afghanistan, it has emerged that, without any announcement by the MoD, two companies of up to 300 troops were deployed in October to help to consolidate gains made against the Taleban in central Helmand.

The Prime Minister will confirm to the House of Commons today that approval had been given to send the two companies from the 2nd Battalion The Princess of Wales's Royal Regiment, which is stationed in Cyprus and acts as a theatre reserve battle group. They were sent soon after the Taleban launched an attack in October on Lashkar Gah, the provincial capital of Helmand. The attack failed but an urgent call was made for more troops, raising the total British military presence to about 8,400.

Mr Brown revealed during the Queen's Speech that Britain was conducting its own review of strategy in Afghanistan. The US has made no formal request for more forces, and this is expected to happen only after Mr Obama becomes President. By publicising a much smaller increase in the number of troops now - an unusual move given that it is a military decision - Mr Brown will be hoping that Mr Obama will read the runes and not put public pressure on Britain to follow suit.

When asked about further British troop deployments next year in Kabul on Saturday, Mr Brown replied that nations other than Britain must bear the burden.

He will repeat this today when he makes a statement to the House of Commons about the redeployment of troops from Cyprus. Mr Brown is cautious about Britain's role in Afghanistan, continually emphasising that the job has become more difficult now that the Taleban have changed tactics and are concentrating on roadside bombings.

Officially the definition of success in Afghanistan for the British military is to protect and support the Afghan Government to the point where the citizens have more confidence in it than in the Taleban.

However, Mr Brown has made clear this weekend that he sees that his priority is different: breaking the “chain of terror” to protect Britain from attacks by terrorists who train in the border region straddling Afghanistan and Pakistan.

— Two former defence chiefs condemned the announcement last week of delays in the programmes to build two 65,000-tonne aircraft carriers for the Royal Navy and 3,000 armoured vehicles for the Army.

Admiral Lord Boyce, Chief of the Defence Staff in 2001-03, criticised the decisions announced by John Hutton, the Defence Secretary. “The security of our country is quite far from being a high priority for this Government and of this the men and women of our Armed Forces are painfully aware.”

Marshal of the Royal Air Force Lord Craig of Radley, Chief of the Defence Staff from 1988 to 1991, said: “Shortages of funds forcing belated reductions, cancellations and delays in critically important defence programmes are inexcusable.”

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