The British military presence in Afghanistan will be almost halved by the end of 2013, Defence Secretary Philip Hammond has told the Commons.
Mr Hammond said the number of UK troops would be cut to about 5,200, paving the way for the withdrawal of most of the forces from the country by the end of 2014.
Numbers are already being cut from 9,500 to 9,000 before Christmas.
The defence secretary said the move was possible because of the "real progress" being made in Helmand, as he delivered his quarterly statement on the situation in Afghanistan on 19 December 2012.
Mr Hammond told MPs: "Our combat mission is drawing to a close but our commitment to them is long-term.
"Progress is clear and measurable and our determination to complete our mission and help Afghanistan secure its future remains undiminished."
Shadow defence secretary Jim Murphy welcomed the government's announcement.
He asked for details on which units will leave and from which parts of Helmand, and sought assurances that those returning would be exempt from "any tranche of future compulsory redundancies".
Former Liberal Democrat leader Sir Menzies Campbell welcomed assurances on troop protection as land forces "are at their most vulnerable" at the time of withdrawal.
But he asked if there would be proper protection of equipment to limit the risk of insurgents "or others with malign intention towards the Afghan government" from using it for their own purposes.
Mr Hammond said the government intended to recuperate "large amounts" of equipment to the UK.
Any equipment not required would be "gifted to the Afghan national security forces, or to the militaries of friendly neighbouring countries, or appropriately destroyed", he added.