MPs are planning to question a top Scotland Yard officer over the force's dropped bid to force the Guardian newspaper to reveal confidential sources for stories relating to the phone-hacking scandal, sources said today.
The Commons Home Affairs Select Committee will summon Deputy Assistant Commissioner Mark Simmons to give evidence in a private meeting on Friday.
The Yard's attempt to identify potential police leaks was widely condemned, with the newspaper's editor Alan Rusbridger describing it as "vindictive and disproportionate".
The Metropolitan Police said it "decided not to pursue" production orders against the broadsheet and one of its reporters after taking legal advice.
It had intended to seek the orders in a court hearing at the Old Bailey on Friday, when the committee's meeting with Mr Simmons will now take place.
Mr Simmons defended the investigation into the leaks today.
He told BBC Radio 4's Today programme: "We've acknowledged and I've acknowledged the role the Guardian has played in the history of what brought us to where we are now, both in terms of its focus on phone hacking itself and indeed its focus on the Met's response to that.
"But in all the glare that has been thrown on to our relationships with the media, we have had to ask ourselves the question about how do we do more to ensure that public confidence in our officers treating information given to them in confidence appropriately is maintained.
"That's why we undertake robust investigation into incidents of leakages."
He added: "I think what's happened is it's thrown into the spotlight the difficulty that we have in getting a new balance in our relationship with the media, in the wake of all the issues that have been aired, very publicly, in recent months."
Mr Rusbridger acknowledged Mr Simmons's remarks about the need for a new balance in relations between the press and the police, but cautioned against moves to curb responsible journalism.
"I just hope that in our effort to clean up some of the worst practices we don't completely overreact and try and clamp down on perfectly normal and applaudable reporting," he told the programme.
"This was a regrettable incident, but let's hope it's over."
The force had said it wanted to identify evidence of "potential breaches relating to misconduct in public office and the Official Secrets Act".
An officer working on Operation Weeting, the force's investigation into phone hacking, was arrested last month on suspicion of misconduct in public office relating to the unauthorised disclosure of information. He has been suspended from duty and is on bail.
The Metropolitan Police's directorate of professional standards consulted the Crown Prosecution Service (CPS), which asked for more information to be provided.
The force stressed that the investigation was "about establishing whether a police officer has leaked information, and gathering any evidence that proves or disproves that".
A spokesman added: "Despite recent media reports, there was no intention to target journalists or disregard journalists' obligations to protect their sources.
"It is not acceptable for police officers to leak information about any investigation, let alone one as sensitive and high profile as Operation Weeting."
Among the evidence said to be sought by the police was information about how the Guardian discovered that the mobile phone of murdered teenager Milly Dowler had been hacked.
The story prompted a massive public outcry and led to the proprietor of the now defunct News of the World, Rupert Murdoch, personally apologising to the Dowlers. The family of the schoolgirl is now set to receive a multimillion-pound payout.
Guardian reporter Amelia Hill, the newspaper's special investigations correspondent, was interviewed under caution by Scotland Yard over alleged leaks from Operation Weeting. She has broken a string of exclusives about the phone-hacking inquiry.
Scotland Yard said the application for production orders was made under the Police and Criminal Evidence Act rather than the Official Secrets Act.
The spokesman said: "The Official Secrets Act was only mentioned in the application in relation to possible offences in connection with the officer from Operation Weeting."
But Mr Rusbridger said: "Threatening reporters with the Official Secrets Act was a sinister new device to get round the protection of journalists' confidential sources."