Former Army commander says 2015 departure could be delayed if Afghanistan is unable to police itself

Afghanistan's police force, whose success and stability is crucial to allowing the government to withdraw British troops, is losing nearly one in five recruits every year, new figures reveal.

Foreign Office statistics show that more than 20,000 officers from the Afghan National Police (ANP), the country's main law enforcement agency, have left over the past year. The Foreign Office figures will cause concern in the armed forces, where the success of the police is seen as the basis for handing control to an Afghan government in 2014 and British troop withdrawal in 2015.

Colonel Richard Kemp, former commander of British forces in Afghanistan, said the figures were "worryingly high" and could play a significant role in determining when Britain can leave.

"In order to get into the condition where we can hand over the country to the Afghans themselves, to manage the security of the country, we need not only a capable army, we need a strong police force," he said. "We are a long way from there. The Afghan national army has still got a long way to go even if it is improving, and the police are some way behind that."

Kemp, who was responsible for training Afghan forces, including the ANP, in 2003, said that the figures would be key in defining when British forces can leave. "Numbers are still important. If we are not getting to where we need to be in terms of either quality or numbers, that is a major concern in terms of being able to hand over to the Afghans in 2014 as is our aspiration," he told the Observer.

The ANP serves as a single law enforcement agency across the country and includes uniformed police, border police, highway police and the criminal investigation department. It had 116,367 officers in October 2010. An estimated 31,343 officers were recruited by the Nato training mission in Afghanistan between January and October 2010.

The attrition rate – including losses caused by deaths, desertion and dismissals, often due to positive drug tests – is currently 18% a year, with monthly attrition at 1.5%, according to figures released to the Labour party.

Shadow foreign secretary Yvette Cooper is pushing for a political process in Afghanistan to support the British military's effort and called for greater emphasis on the retention of officers.

"For the Afghan strategy to work, our troops need to be able to hand over to stable, well functioning Afghan security forces," she said. "Simply increasing their numbers isn't enough and needs to be accompanied by stronger work to retain properly trained officers who can do the job. We also need a durable political settlement which is sustainable at local level."

The problem of retaining police officers was highlighted by Lieutenant-General William Caldwell last year when he claimed that drug abuse, illiteracy and desertion are just some of the problems among Afghanistan's police. He said the vast majority of ANP members still "did not know the law they were responsible to enforce".

His review added: "Not unexpectedly, most Afghans had come to view the ANP as lawless armed men, rather than trusted law enforcement officials."

David Cameron wants the handover completed by the end of 2014, allowing British troops to leave combat roles by 2015. Last week the prime minister announced further funding for the Afghan police and said this was a vital component of the timetable.

A series of internal Foreign Office papers disclosed in March showed the deep concerns of British officials about the standard of recruits to the ANP. Defence ministry sources claim that a wage increase has closed a pay gap between the police and the army. They also say that more effective training programmes have raised standards of leadership and discipline.

A government spokeswoman said the figures reveal an improvement which will be built on in coming months: "The International Security Assistance Force, working with the Afghan government, is building a strong and effective Afghan National Police force as part of the international effort to give Afghanistan the ability to provide its own security and governance.

"This work is currently ahead of schedule for recruiting 134,000 Afghan police by the end of 2011 and a key push going forward is to reduce levels of attrition which have already been decreasing consistently and are now very close to the target of 16.8%. The monthly attrition rate for the Afghan Uniformed Police, who form the majority of the ANP, is even more encouraging at 1.1% – well within set targets. These reductions have been achieved through a range of methods implemented by the Afghan government in partnership with the international coalition, including increases in police pay."