The legitimacy of the police service is at risk unless the government makes a "game changing" intervention to increase the number of ethnic minority police officers, the Met Police Commissioner believes.

Sir Bernard Hogan-Howe's stark statement came in his response to the College of Policing's leadership review.

Yesterday the force revealed that its policy of banning applications from those who live outside London had increased the rate of black and ethnic minority (BME) recruitment from 12 to 26 per cent in a year.

Just under 12 per cent of officers in the force are now from BME communities, compared to 40 per cent of the population of the capital.

The commissioner's letter to Chief Constable Alex Marshall, written in April, says that while ideas such as the London residency test have helped, they do not go far enough.

"There has to be an acceptance of the fact that, for all our best intentions, positive action alone is not going to deliver a representative workforce in anything like a reasonable timeframe.

"In a leadership context, if we just allow current arrangements to continue it will require many tens of years before we see anything like a representative leadership cadre.

"I would strongly encourage you to be stronger on this point. Police legitimacy will be at risk unless we collectively tackle this issue. A 'game changer' is needed, and we need government to help here," he said.

The letter was released following a Freedom of Information Act request by PoliceOracle.com.

In an interview last year, Sir Bernard re-iterated his call for a change in the law so that the force could take on BME and white recruits in a 50:50 ratio, based on the Northern Irish system used for Protestants and Catholics, in order to speed up the process.

During the general election campaign Prime Minister David Cameron said he wanted to see a fifth of all new police recruits come from BME backgrounds by 2020.

Policing Minister Mike Penning had earlier told PoliceOracle.com that he was "open minded" about Sir Bernard's call for a quota system.

However the government is yet to set out any policies to address the issue, and recruitment is frozen in many forces.

Her Majesty's Inspectorate of Constabulary will be taking the representative nature of forces into account in the legitimacy category of its next round of PEEL assessments, which are now underway.

Janet Hills, chairman of the Metropolitan Black Police Association, told PoliceOracle.com yesterday that she believes such a change in the law would not necessarily address the full issue.

"There also needs to be a lot of work done in the community itself. We always talk about trust and confidence issues, particularly among young people, so we can't only focus efforts on one area," she said.

"There are a lot of legitimacy issues around why people won't come in."

Last year the College of Policing conducted surveys which revealed a split among BME officers over whether they support the use of positive discrimination.

College lead on black and minority ethnic progression, Superintendent Manjit Thandi, said yesterday the organisation was carrying out several initiatives including providing forces with "action plans to improve BME representation and progression".

"Although the number of BME officers has risen by more than 350 since 2011, bringing the total in 2015 to nearly 7,000, more needs to be done and as part of our ongoing work the College is holding a conference later this month on unconscious bias to help forces identify and mitigate the issue and address existing barriers," he added.

Workforce statistics released earlier this year show that 28 forces have less than ten officers who identify as "black or black British".

Labour's London Mayor candidate Sadiq Khan has called for a change in the law to allow the Met to introduce a quota system to boost BME representation.