The new head of the Army is warning that Britain's mission in Afghanistan could last in some form for up to 40 years.

General Sir David Richards, who becomes Chief of the General Staff later this month, said in a newspaper interview: "I believe that the UK will be committed to Afghanistan in some manner - development, governance, security sector reform - for the next 30 to 40 years."

He also played down the issue of equipment shortages as he prepares to take office, in direct contrast with the man he will be replacing as Chief of the General Staff (CGS), saying he would not be presenting the Government with a "shopping list" of kit.

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Current army chief General Sir Richard Dannatt vowed to do just that amid mounting British casualties and controversy over the adequacy of equipment such as armoured trucks and helicopters last month.

In an interview with The Times, General Richards said: "It is impossible to say whether having more equipment of a particular kind would lead to less casualties, and pretty fruitless speculating about it.

"The enemy's tactics will always reflect, and try to exploit, how we operate - my American comrades first taught me the adage, 'The enemy has a vote' - and our own tactics must reflect the equipment and troop numbers we have.

"It is a truism to state that the more we have, the more we can do."

Asked if he would be presenting a "shopping list" for military equipment on his first day in office, the general answered: "I will not."

But he said the Army and the Government needed to ensure "we continue to respond flexibly and quickly to the evolving requirements of our campaign in Afghanistan."

The 57-year-old, who calls himself a "seat-of-the-pants soldier", was commander of Nato's International Security Assistance Force (ISAF) in Afghan capital Kabul in 2006.

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That made him the first British officer to command American forces since the Second World War.

He takes over as CGS on August 28, and he will hold the post for three years.

The general told The Times that "nation-building" in Afghanistan would take time, and that "there is absolutely no chance of Nato pulling out".

"It is not just reconstruction; jobs and simple governance that works are key, and there has to be a strong reconciliation element to the latter," he said.

"The Army's role will evolve, but the whole process might take as long as 30 to 40 years."

Gen Richards also said he believed strongly that the mission in the country was "winnable".

"Demanding, certainly, but winnable," he said.

"And when people say, 'How can you use the term "win"?' I retort, 'Well, I will certainly know if we have lost'.

"Can you imagine the intoxicating effect on militants if we were defeated? Can you be certain there would not be an export of terrorism to the streets of London? It's a risk we should be very wary of taking.

"As I have said many times, everyone involved needs to realise it will take a long time and considerable investment. We must remember, though, that we are not trying to turn Afghanistan into Switzerland."

Despite the recent spate of British casualties in the theatre - a record 22 in July and four so far this month - he stressed that morale was high among the troops.

"I'm in regular contact with our troops in Afghanistan. Knowing them well, I am not surprised, but their morale is high. What they want to do is succeed in their mission. Firstly, because they believe in it. Secondly, to ensure those who have made the ultimate sacrifice on behalf of our nation have not done so in vain. The last thing they want is for us all to go wobbly on them."

Gen Richards added: "Nor should you think the Taliban are finding it easy. We know they are not. We can and are outfighting them."