Sir David says UK troops will offer support in Afghanistan for many years
Britain will be "militarily engaged" in Afghanistan for a further five years, the head of the Army has said.
General Sir David Richards told the Daily Telegraph, while on a visit to Helmand, that he expected the military conflict to "trail off in 2011".
But British troops will continue in training and support roles, he said.
He also warned that coalition troops could not afford to fail and said UK forces now "for the first time" had the resources they had wanted.
Sir David said in August that he believed the UK would be committed to Afghanistan "in some manner" for the next 30 or 40 years, possibly through roles in development, governance and security sector reform.
Sir David said: "The combat role will start to decline in 2011, but we will remain military engaged in training and support roles for another five years, and we will remain in a support role for many years to come."
Speaking on a visit to Afghanistan during Operation Moshtarak, which is an ongoing offensive to attack the Taliban, he said the campaign was showing some "very optimistic signs".
He added: "A year ago the Taliban thought they had us on the run, but now the tables have turned. They are under relentless pressure and they are now having some serious thoughts about continuing the fight.
"I do not think we can afford to fail in Afghanistan because of the intoxicating effect failure will have on those militants who oppose democracy and our freedoms.
"The Taliban is now beginning to realise that they can lose this war, which was not the view they had a year ago."
Sir David's comments come after the deaths of three British servicemen in three days.
A soldier from 28 Engineer Regiment, attached to the Brigade Reconnaissance Force, died on Friday after being caught in a blast near a check point in Nad Ali, Helmand. He has not yet been named.
Rifleman Martin Kinggett from A Company 4 Rifles was shot dead in Sangin on Thursday and Senior Aircraftman Luke Southgate died in an explosion north of Kandahar airfield on Wednesday.
A total of 266 British service personnel have died since the conflict began.