Defence Secretary Philip Hammond is considering plans to bring back some British troops from Afghanistan earlier than expected, he has revealed.
Mr Hammond said there was "a bit of rethinking" about soldier numbers after military commanders reported that Afghan forces were taking on the "lion's share" of the combat role.
Prime Minister David Cameron has repeatedly said he is keen to avoid a "cliff-edge" on troop withdrawal in 2014, the date when all UK combat troops are due to be out, but insisted the decision should be based on Afghan progress.
Mr Hammond said he had been privately pushing "for keeping force levels as high as possible for as long as possible" earlier this year but said military commanders were "surprised by the extent to which they have been able to draw back and leave the Afghans to take the lion's share of the combat role".
In an interview with the Guardian in Camp Bastion, Helmand, he said: "I think there is a bit of a rethinking going on about how many troops we do actually need... there may be some scope for a little bit more flexibility on the way we draw down, and that is something commanders on the ground are looking at very actively."
Around 500 British troops are due to return home by the end of this year, leaving a further 9,000 to return by the end of 2014.
He added: "I think that the message I am getting clearly from the military is that it might be possible to draw down further troops in 2013. Whereas six months ago the message coming from them was that we really need to hold on to everything we have got for as long as we possibly can. I think they are seeing potentially more flexibility in the situation.
"Talking to senior commanders you get a clear sense that their view of force levels is evolving in light of their experiences."
The Defence Secretary insisted Britain would not be "spooked" by the run of "green on blue" attacks - when Afghans turn on international troops. He added: "We have to be clear why we came here in the first place. I believe very clearly that if we are going to ask British troops to put themselves in the firing line, we can only do that to protect UK vital national security interests."
Downing Street said that David Cameron had already made clear that he expects to be able to withdraw further troops from Afghanistan in 2013, but said that no decisions have yet been taken.