Assistant Commissioner John Yates admitted in 2009 that Met police officers who had been prosecuted for accepting cash from newspapers in exchange for information could still be working.

John Yates - Reuters

Assistant commissioner John Yates, who headed the first investigation into the phone hacking enquiry in 2006, confirmed during a meeting of the Metropolitan Police Authority (MPA) in July 2009 that an undisclosed number of officers had received money from unspecified media organisations.

Mr Yates, now Scotland Yard's counter-terrorism chief, added that it was possible officers had kept their posts after being prosecuted.

At the meeting, Jenny Jones, an MPA member, asked Mr Yates: "(Have) police officers taken money either to give information or to stop exploring criminal activities?"

Mr Yates replied: "Does ever happen? Yes, of course it does happen on occasion, and there have been instances in the past when it has happened and we have investigated it very thoroughly. But are we looking at it at the moment? No, we are not."

He added: "Several police officers, past and present, either ex or current, have over the past number of years been prosecuted for selling information like off the PNC and the like."

Several police officers, past and present, either ex or current, have over the past number of years been prosecuted for selling information like off the PNC and the like - Assistant commissioner John Yates

Boris Johnson, the Mayor of London, then asked Mr Yates how it was possible for a policeman who had either been disciplined or convicted of accepting money for information - a crime which could result in a prison sentence - could be allowed to keep their jobs.

"It is possible depending on the level of offending. It will be dealt with in a proportionate way in terms of what they have done," he added.

The news follows revelations that News International have email confirmation that such payments have been made, and raises questions about why an investigation into the practice was not launched years ago.

Mrs Jones said she would use the next meeting of the MPA later this month to ask police whether any of the officers in the original investigation into phone hacking allegations, or those in the current Operation Weeting and Operation Elveden - which is investigating allegations of inappropriate payments to police - had themselves ever received payments from a newspaper in the past.

"There is a public suspicion that this has been a widespread practice in the past with the police providing tip-offs and nuggets of information to journalists and photographers," she said.

"I would be happy with a simple statement being made by officers of all ranks involved in both the current investigation and the initial investigation, that they have not received such payments at any point in their careers."

On Friday, Sir Paul Stephenson, the Metropolitan Police Commissioner, released a statement confirming Operation Weeting had been in receipt of at documents relating to alleged payments to officers.

The statement read: "I can confirm that on 20 June, 2011 the MPS was handed a number of documents by News International, through their barrister, Lord Macdonald QC.

"Our initial assessment shows that these documents include information relating to alleged inappropriate payments to a small number of MPS officers.

"At this time we have not seen any evidence requiring a referral to the Metropolitan Police Authority (MPA) in respect of any senior officer."