The National Union of Journalists has told parliament that police misuse of the Regulation of Investigatory Powers Act to snoop on journalists and their sources is “systemic and institutionalised” and is doing “irreparable damage” to the industry.

Michelle Stanistreet, the NUJ’s general secretary, told the home affairs select committee that police were routinely bypassing the need for judicial scrutiny to discover journalistic sources by using Ripa to go through phone records and other data.

Keith Vaz, chairman of the committee, said he had “concerns” about the use of the act, passed in 2000 and repeated calls for a review. He called for the inquiry after it emerged that police investigating the former MP Chris Huhne’s speeding fraud secretly obtained a Mail on Sunday reporter’s phone records without his consent. It also emerged that police investigating the Plebgate saga obtained the telephone records of the political editor of the Sun, Tom Newton Dunn.

Stanistreet said these stories were just the “tip of the iceberg”, with several police authorities dragging their heels over Freedom of Information requests about their use of such powers.

The committee also heard from three senior police officers who denied any misuse of the act. Mick Creedon, Chief Constable of Derbyshire police, said the only journalistic sources they were interested in were “corrupt individuals”. “We’re not interested in journalistic sources... I can’t understand why we would be interested,” he added.

His colleague, Assistant Chief Constable Richard Berry, national policing lead for communications data, said communications “data and traffic” is “not journalistic material”, a comment likely to raise eyebrows in the wake of the Edward Snowden NSA leaks and revelations about the use of metadata some 14 years after the act was passed.

The committee heard that some clarification was needed to determine what a “journalist” was in the light of citizen journalism and social media.

There are seven reasons for using Ripa, the police officers said, adding that it had been “misreported” that it was used simply to chase terrorists.

The NUJ and other freedom of the press campaigners believe the powers within Ripa are in contravention of article 10 of the European convention on human rights, which promises the right to freedom of expression. Without this protection, Stanistreet argued, the public will no longer trust the press with important stories. The misuse of Ripa was a bombshell for the industry with long-term consequences, she warned.

The union is backing the Press Gazette’s Save our Sources campaign on the issue. The number of applications to use Ripa has exploded in recent years, with more than 6,000 a year in 2013 compared with just over 60 in 2002, according to the committee.