Amelia Hill was questioned under caution by police in an inquiry into alleged leaks of information from Operation Weeting

. Photograph: Katherine Rose

The National Union of Journalists and a respected media watchdog have criticised the questioning of a Guardian journalist in an inquiry into alleged leaks of information from Operation Weeting, the investigation into phone hacking at the News of the World.

It emerged on Wednesday that Amelia Hill, a reporter involved in a number of the Guardian's key phone-hacking revelations over recent weeks, was questioned under caution several days ago in a case that raises concerns about attempts to criminalise contact between journalists and off-the-record sources.

Last month a 51-year-old detective constable was arrested in connection with alleged leaks from the Scotland Yard phone-hacking investigation. At the time there were reports that the officer had passed information to the Guardian, but the newspaper said it had "no comment to make on the sources of our journalism".

Michelle Stanistreet, the general secretary of the National Union of Journalists, said that there was "a vital journalistic principle at stake here" and that "it is outrageous that an allegation of off-the-record briefings is being treated as a criminal matter".

She added: "There is a clear distinction between legitimate off-the-record interviews and the illegitimate payment of bribes."

Martin Moore, the director of the media watchdog the Media Standards Trust, said that in the light of the phone-hacking scandal it was becoming "increasingly important to sustain and defend journalism in the public interest". He said that it was "not the time to be threatening public interest journalism" by the police moving to question reporters such as Hill.

The Guardian said in a statement: "We can confirm Amelia Hill has been questioned in connection with an investigation into alleged leaks." The newspaper argued that the case could have lasting repercussions for the way journalists deal with police officers. The statement added: "On a broader point, journalists would no doubt be concerned if the police sought to criminalise conversations between off-record sources and reporters."

Although the paper said it would not comment on any specific confidential source, a spokesman said Hill had never paid a police officer for information.

The police investigation into leaks from Operation Weeting has been going on for several weeks.

Meanwhile, Raoul Simons, 35, the deputy football editor of the Times, became the 16th person to be arrested as part of the phone hacking enquiry.

Simons, who had joined the Times from the Evening Standard in August 2009, is understood to have been arrested at 5.55am on suspicion of conspiring to intercept communications. He was released on police bail until a date in October.

He was not arrested by prior appointment. He was taken to a north London police station and questioned on suspicion of conspiracy to intercept voicemail messages, contrary to Section 1 (1) of the Criminal Law Act 1977.

Hill's police interview comes amid growing pressure to clamp down on contacts between officers and journalists following the News of the World phone hacking scandal, which has spread out into wider allegations of police corruption.

Emails from News International allegedly imply that journalists on the now closed Sunday tabloid bought copies of Buckingham Palace's private phone directory from a royal protection officer.

Following those revelations, an inquiry by Her Majesty's Inspectorate of Constabulary is examining "alleged corruption and abuse of power" in police relationships with the media, and Elizabeth Filkin, the former parliamentary commissioner for standards, heads a group drawing up a framework for how police officers handle their relationships with reporters. Both inquiries are considering whether communication between police officers should be officially monitored and recorded by a press officer.

The questioning of Hill has similarities to a case police mounted against Sally Murrer, a reporter on the Milton Keynes Citizen, and a former Thames Valley police detective, Mark Kearney, which was thrown out. Kearney had been accused of leaking information to Murrer. The collapse of the case was widely seen as a victory for journalistic freedom.

It was reported meanwhile that Andy Coulson, the former editor of the News of the World and the prime minister's former personal communications director, is refusing to appear before a Commons select committee that is investigating phone-hacking.

His solicitors have written to the culture, media and sport committee declining an invitation to appear, citing "concerns" about "parallel inquiries and investigations and the publicity generated by them".

He has consistently denied knowing that phone hacking took place but last month a previously unseen letter from Goodman emerged that claimed phone hacking was "widely discussed" at editorial conferences until Coulson banned mentions of it. Goodman's letter also claimed that Coulson had offered to let him keep his job if he agreed not to implicate the paper in hacking when it came to court.

Coulson resigned from the News International paper in 2007 after its former royal editor Clive Goodman was jailed on phone-hacking offences.

It also emerged yesterday that MPs on another committee have been told that News International asked a technology firm, HCL, to delete emails and other documents 13 times since 2009.

Technology company HCL, which provides services under contract to News International, informed the Commons home affairs committee in August that it was aware of the deletion of hundreds of thousands of emails on nine occasions between April 2010 and July 2011, but said it did not know of anything "untoward" behind the requests. Yesterday, HCL's solicitor, Stuart Benson, contacted the committee again to say that a further four requests had come to light - one of which related to the deletion of emails from an inbox of a user who had not accessed his account for eight years.