The head of the armed forces has given a clear warning to ministers that troops should not be transferred from Iraq to Afghanistan when Britain's military commitment there is scaled down next year.
Chief of the Defence Staff, Air Chief Marshal Sir Jock Stirrup, said it was "crucial" for the armed forces to experience a reduction in the tempo of operations over the coming period, to recover from several years of overstretch.
His comments come as the US President-elect Barack Obama prepares to order a significant increase in troop numbers in Afghanistan in the hope of finally quelling the Taliban insurgency.
The Foreign Secretary, David Miliband, indicated that the UK, whose 8,100 troops in Afghanistan make it the second-largest contributor to the international force, will expect other Nato countries to take up a bigger share of the burden in any US-led "surge". And he appeared to rule out the commitment of British troops to the peace-keeping force in the Democratic Republic of Congo, insisting: "That is not on the agenda."
Sir Jock said he was "optimistic" that 2009 would see a "significant reduction" in the UK's 4,000-strong Iraq contingent, as the fundamental change of mission promised by Gordon Brown comes into effect. But he cautioned that this would not mean that thousands more servicemen and women become available for deployment to other hotspots.
Sir Jock told BBC1's Andrew Marr Show: "I have said for a very long time the British armed forces are stretched. We are doing more than we are structured and resourced to do in the long term. We can't continue ad infinitum.
"We have to put ourselves back into balance. It is crucial that we reduce the operational tempo for our armed forces. So it can't be – even if the situation demanded it – just a one-for-one transfer from Iraq to Afghanistan. We have to reduce that tempo."
Sir Jock warned: "I am a little nervous when people use the word 'surge' as if this were some sort of panacea. What we are quite clear about is that we need more military force in Afghanistan – the Nato combined statement of requirement has yet to be fully met. Everybody needs to do their share. In Iraq and Afghanistan, we are shouldering a burden which is more than we are able to shoulder long term, so we expect others to take up their share of that burden."
Asked if Britain had the capacity to offer forces for Congo, Sir Jock replied: "The United Nations has 17,000 troops on the ground, so there are more than enough there already."
Asked if President-elect Obama's plans to step up the pace of operations in Afghanistan will require an increase in the size of Britain's commitment there, Mr Miliband told The Andrew Marr Show: "Not necessarily, no."
He added: "President-elect Obama has said he wants two new brigades to go in, there are an extra 1,500 French troops and the Germans are increasing the number of their troops. As the second-largest contributor of troops in Afghanistan, we don't want to bear an unfair share of the burden.
"More foreign troops on their own are not the answer. It needs to be an approach that combines a serious security presence with the development of the country. It's got to be a civilian surge as well as a military surge."