Gordon Brown has rejected the advice of both his Defence Secretary and military chiefs by refusing to send 2,000 more troops to Afghanistan to boost the permanent British presence in Helmand province to more than 10,000.

Despite pleas from commanders in southern Afghanistan for more “boots on the ground” to help to hold territory won against the Taleban, the Prime Minister has sided with the Treasury and has ruled that the total force must remain at the present level of 8,300.

The decision, after months of wrangling between the Ministry of Defence, Downing Street and the Treasury, has shocked and gravely disappointed military chiefs. John Hutton, the Defence Secretary, also put his full weight behind their recommendation to send long-term reinforcements.

Mr Brown confirmed that the only troop boost he had approved was the temporary deployment of a battalion of 700 soldiers for a four-month period leading up to and beyond the presidential elections on August 20.

“Apparently the Prime Minister thinks that with the planned uplift of 17,000 American combat troops going to Afghanistan, he is able to take the decision to keep Britain’s permanent force to 8,300,” officials said.

The decision will also bitterly disappoint the Americans, who had been led to believe that a mini-surge of British troops was due to be announced. President Obama had spoken to Mr Brown about Britain sending more troops, and Nato military chiefs had fully expected the British Government to respond positively.

Mr Brown’s change of mind, under Treasury pressure, will be a bitter blow for General Sir Richard Dannatt, the head of the Army, who revealed in an interview with The Times in March that he had earmarked up to 2,000 troops for Afghanistan and that he was awaiting a political decision. The troops, all from 12th Mechanised Brigade, have been training on Salisbury Plain and are now ready for an overseas operation.

The Prime Minister was briefed on the troop situation on Monday when he flew to Afghanistan where he met Brigadier Tim Radford, commander of the newly arrived 19 Light Brigade, at his headquarters in Lashkar Gah.

In key places such as Musa Qala in the north, the brigade has a battle group of just 700 soldiers, only a proportion of whom are combat infantry-men capable of taking on the Taleban.

Military commanders admit that they can only try to consolidate achievements made by previous battle groups but cannot risk pushing too far out of the district against the Taleban front line because of the limited resources and the danger of being too thinly deployed. This lesson was learnt in 2006 when a platoon of about 30 paratroopers from 16 Air Assault Brigade was dispatched to protect the district centre in Musa Qala and came under sustained attack by the Taleban. The British troops were forced to withdraw and despite a supposed deal with the local tribal elders to run the town, the Taleban were soon back. A full-scale attack by British and Afghan troops in December 2007 was needed to seize control of the town.

In Garmsir, in southern Helmand, the same lack of troop resources has limited the options for taking the fight to the Taleban. The Americans are going to change all that when they send thousands of the US surge troops to fight the Taleban down to the border with Pakistan.

Camp Bastion, the main British base in central Helmand, is already accommodating 3,000 US Marines, and 7,000 more are due to arrive by the end of May, dwarfing the British presence in a province that is supposed to be Britain’s area of responsibility. The Pakistani military seized a key northwestern town yesterday after air strikes killed dozens of insurgents in a major offensive to halt the Taleban advance that has brought the militants close to the capital. Army commandos dropped by helicopters behind Taleban lines swiftly recaptured Dagar, the main town in Buner district, which was overrun earlier this month by insurgents advancing from Swat valley, a militant stronghold. Analysts said that Pakistan’s military action in Buner could reassure President Obama, who would be meeting President Zardari in Washington on May 6.

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