Scotland Yard has defended its attempt to force The Guardian to reveal its sources for stories relating to the News of the World phone hacking scandal.
The Metropolitan Police is trying to use the Official Secrets Act to make the newspaper reveal its confidential sources to identify potential police leaks.
The force has applied for a production order against The Guardian and one of its reporters "in order to seek evidence of offences connected to potential breaches relating to Misconduct in Public Office and the Official Secrets Act".
"The application is about the MPS seeking to identify evidence of potential offences resulting from unauthorised leaking of information," it said in a statement.
But the paper's editor Alan Rusbridger strongly condemned the move as "vindictive and disproportionate" and said the paper would resist it "to the utmost".
Among the information the police are said to be seeking is the source of The Guardian's report disclosing that the mobile phone of murdered teenager Milly Dowler had been hacked. The story prompted a massive public outcry and led to the former proprietor of the now defunct News of the World, Rupert Murdoch, personally apologising to the Dowler family.
The Met said it applied for the production order as part of its investigation into phone hacking, adding: "Operation Weeting is one of the MPS's most high profile and sensitive investigations so of course we should take concerns of leaks seriously to ensure that public interest is protected by ensuring there is no further potential compromise. The production order is sought in that context.
"The MPS can't respond to the significant public and political concern regarding leaks from the police to any part of the media if we aren't more robust in our investigations and make all attempts to obtain best evidence of the leaks."
The statement said that the Met was not seeking to use the law "to prevent whistle blowing or investigative journalism that is in the public interest".
The Guardian said the police intended to go before a judge at the Old Bailey on September 23 to apply for an order under the Official Secrets Act 1989 requiring it to hand over documents relating to the source of information for a number of articles.