The Guardian claims police are seeking a court order to have documents released disclosing sourcesCopyright: Michael Bruntonspall on Flickr. Some rights reserved
The Guardian has reported that officers are trying to secure documents relating to sources for a number of articles, claiming the Act may have been breached in its coverage of stories such as the alleged hacking of Milly Dowler's phone.
The Met's application for the order is due to take place at the Old Bailey on Friday (23 September), and will be heard in private in chambers.
In a statement Guardian editor Alan Rusbridger said the paper "shall resist this extraordinary demand to the utmost".
The National Union of Journalists has also offered its support to the Guardian, with general secretary Michelle Stanistreet quoted in the newspaper's report as saying journalists behind some of the coverage "should be congratulated rather than being hounded and criminalised by the state".
Chief executive of the Index on Censorship also criticised the "shocking" move.
"The Guardian is to be praised for pursuing the phone hacking case where the Metropolitan police failed — and for exposing the extent of the scandal. Protection of sources is a crucial tenet of investigative journalism and must be respected."
This news follows the questioning under caution of Guardian reporter Amelia Hill by police officers investigating an alleged leak of information from the force's phone-hacking team, Operation Weeting.
This leak is believed to relate to information about the arrest of former News of the World Hollywood correspondent James Desborough, which was covered in the Guardian by Hill.
The day after her report was published a 51-year-old police officer was arrested by members of the Met's anti-corruption team over "unauthorised disclosure of information".
The Met police began two internal investigations this month into contact between officers and journalists, which will look at whether communications between them should be officially monitored and recorded.
There was no comment available from the Metropolitan Police at the time of writing.
Update: The Metropolitan Police have now issued a statement confirming their application for a production order against the Guardian and one of its reporters:
"The application is about the MPS seeking to identify evidence of potential offences resulting from unauthorised leaking of information.
"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.
"We pay tribute to the Guardian's unwavering determination to expose the hacking scandal and their challenge around the initial police response. We also recognise the important public interest of whistle blowing and investigative reporting, however neither is apparent in this case."
The MPS added that it "does not seek to use legislation to undermine Article 10 of anyone's Human Rights and is not seeking to prevent whistle blowing or investigative journalism that is in the public interest, including the Guardian's involvement in the exposure of phone hacking".