The price of peace in Afghanistan emerged amid warnings that British forces will have to remain in the country for up to five years in a support role, even after the withdrawal of combat troops in 2014.

Efforts to rebuild Afghanistan after more than a decade of conflict could include a series of concessions to the Taliban designed to secure a lasting peace, after Nato leaders concluded that they could not defeat the insurgents militarily.

As David Cameron talked up a political solution during a whistle-stop visit to Afghanistan yesterday, senior British military sources confirmed that the concessions could see Taliban members in power, and even the acceptance of their fighters into the Afghan regular forces.

Officials also suggested that the country's new constitution could be partly rewritten to appease the Taliban. They claim the peace process could be rejuvenated before Afghanistan elects its new president in April.

Mr Cameron visited frontline troops in Helmand Province to mark Armed Forces Day yesterday as Britain's top commander in Afghanistan said the West should have attempted to enter talks with the Taliban a decade ago. General Nick Carter, deputy commander of the Nato-led coalition, told The Guardian that when the Taliban were "on the run" in 2002, months after being toppled, they could have been persuaded to sit round the negotiating table.

Senior military sources told The IoS yesterday that hundreds of British forces will remain in the country for "three to five years", in a "support role" designed to help Afghanistan's new democracy survive.

The Prime Minister made clear his views that the Taliban had a key part to play in the new Afghanistan, following a meeting with President Hamid Karzai in Kabul. But he insisted that the insurgents would have to lay down their arms and come to the negotiating table.

"The Taliban, watching all this progress, are beginning to realise they cannot secure a role in Afghanistan's future by terror and arms, but by giving up their arms and engaging in a political process," he said.

The intervention comes amid continuing attempts to lock the Taliban into the peace process, 12 years after they were ousted from power by an international military coalition.

The Afghan police and army have developed to the point where they have taken responsibility for security in their own country. But experts still warn that the new security forces could be vulnerable to a sustained insurgent campaign.

A senior British official said yesterday that the UK had been seeking a political accommodation in Afghanistan for "four or five years", since it became clear that a military victory over the Taliban was unlikely.

He added: "Some of the Taliban who are currently detained; if there was a political settlement, they could be released. We could give them uniforms and make them part of the Afghan armed forces. You have got to give them something worthwhile to stop them fighting."

But a move to rehabilitate Taliban fighters into the mainstream of Afghan society would be controversial, particularly among the relatives of the 444 British servicemen and women killed there since 2001.

Yet senior British military and diplomatic officials insist that a political solution is now the best option. One said last night: "If we were to go down this route, then clearly it would need to be done with the support of the British people. We would need to explain that this is a way to maximise our legacy. If we can achieve these goals, I hope that those who have lost loved ones during this conflict will believe that their loved ones have not died in vain."

With just a year to go before combat troops pull out in 2014, there are worrying signs that the Afghan army is far from ready to take over. Tens of thousands of soldiers are leaving its ranks – the casualties of an attrition rate currently running at 30 per cent a year.

Having troops in a "support role" could range from having special forces to trainers and people to maintain equipment, according to Major General Julian Thompson, a former commander of the Royal Marines. "Even if you are sitting in the Afghan equivalent of Sandhurst, you are not necessarily totally safe."

Lord West, a security minister under Labour, warned: "One of the issues in Afghanistan is they don't like foreigners being there, and it seems to me that we need to get out of this place and let the politics run it without us having to be immersed in among it all."

General Sir David Richards, outgoing Chief of the Defence Staff, said in 2009 that the mission to stabilise Afghanistan could take 40 years.

Additional reporting by Jonathan Owen

Memorial planned

David Cameron unveiled plans to British troops in Lashkar Gar for a permanent memorial to those who have lost their lives in Afghanistan since 2001. The monument for the 444 British personnel killed in the conflict will be built at the National Memorial Arboretum in Staffordshire and will be funded by fines paid by banks following the Libor scandal.

The £300,000 allocation comes from  almost £3.8m of funding for charities that support military families and programmes providing mental health support for veterans.

A new memorial will be erected in sand coloured stone to honour all those who have died serving the UK in Afghanistan. The existing memorial in Camp Bastion will be dismantled and as much of it as possible will be used in the new memorial which will provide a focal point for remembrance for families, friends and comrades. The memorial will be built over the next 18 months and dedicated once combat operations in Afghanistan have ended.

The Prime Minister said: “Britain must never forget those who gave their lives in Afghanistan. A Bastion Memorial Wall back at home deserves every penny of this funding. It will give us a permanent place to remember those who made the ultimate sacrifice in Afghanistan and to show how proud and thankful we are for all they gave serving our country. They must never be forgotten.”

Almost £2.5 million has been awarded to programmes supporting treatment and awareness of mental health issues for veterans, including the Warrior Programme for Veterans and Families which will receive just over £930,000 to further their efforts to support veterans moving into civilian life.

Veterans Aid, whch last year assisted 458 veterans in crisis, will be able to expand their substance abuse and mental health treatment programmes for homeless and in-need veterans with an award of £160,000.

Brian Brady