The chairman of the Commons intelligence and security committee has called for "the great majority" of British troops to be pulled out of Afghanistan.
Kim Howells, Labour MP for Pontypridd, said in an article in the Guardian that the UK should instead concentrate resources on securing its borders.
He was a Foreign Office minister until last year and had responsibility for Afghanistan in that role.
"Seven years of military involvement and civilian aid in Afghanistan have succeeded in subduing al-Qaida's activities in that country, but have not destroyed the organisation or its leader, Osama bin Laden," he wrote.
"If we accept that al-Qaida continues to pose a deadly threat to the UK, and if we know that it is capable of changing the locations of its bases and modifying its attack plans, we must accept that we have a duty to question the wisdom of prioritising, in terms of government spending on counter-terrorism, the deployment of our forces to Afghanistan," he wrote.
"It is time to ask whether the fight against those who are intent on murdering British citizens might better be served by diverting into the work of the UK Border Agency and our police and intelligence services much of the additional finance and resources swallowed up by the costs of maintaining British forces in Afghanistan."
Howells said it would be better to bring home "the great majority of our fighting men and women and concentrate on using the money saved to secure our own borders".
He proposed more focus on gathering intelligence on terrorist activities inside Britain, expanding intelligence operations abroad, co-operating with foreign intelligence services, and countering "the propaganda of those who encourage terrorism".
There are 9,000 British troops in Afghanistan and a further 500 have been pledged if the Afghan authorities meet certain conditions.
Defence secretary Bob Ainsworth told the BBC he disagrees with Howell's analysis.
"We cannot secure ourselves at the borders of Great Britain... if Afghanistan is not secured, then Pakistan will not be secure and Great Britain will not be secure," he told The World At One.
"We are there because this mission is inextricably tied to our own safety in the United Kingdom."


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