Overall, Britain will have 6,100 military personnel involved with Afghanistan. These come on top of 13,500 in Northern Ireland, 3,400 in Cyprus, 2,800 in Kosovo, 1,600 in Bosnia, 1,100 in the Gulf region to police Iraqi no-fly zones, 1,200 in the Falklands, 400 in Sierra Leone, 400 in Gibraltar and 500 in various United Nations operations.

The Ministry of Defence said the level of commitments was "still manageable". However, service chiefs have warned they would not be able to keep up the recent tempo without additional resources.

Royal Marines and army soldiers will form a full infantry battle group that will link up with US and Canadian forces in Afghanistan to form a US-led brigade of 5,000 to 6,000 troops devoted to rooting out al-Qaeda and Taliban remnants.

The UK force will be built around 45 Commando of the Royal Marines, based at Arbroath in Scotland, and will include the headquarters of 3 Commando Brigade, led by Brigadier Roger Lane.

Some 200 members of 45 Commando, already aboard the helicopter carrier HMS Ocean in the Arabian Sea, will deploy to Bagram air base north of Kabul where they will be joined by other elements being sent from Britain. These include 7 Battery of 29 Commando Regiment, Royal Artillery, also based at Arbroath and equipped with 105mm guns.

Engineering and logistics elements will come from 59 Independent Commando Squadron, Royal Engineers, based at Chivenor, north Devon, and parts of the Commando Logistics Regiment based at Chivenor. Three Chinook helicopters are being sent from RAF Odiham, Hampshire.

They will be separate from the 1,800 UK troops in Kabul as part of the International Security Assistance Force, though Britain's contribution is likely to drop as other countries take over some of its functions.