A Holyrood committee has written to the UK surveillance watchdog as a first step towards launching a probe into Police Scotland unlawfully spying on journalists’ sources.

MSPs wrote to the Interception of Communications Commissioner (IOCCO) last week as part of an initial scoping exercise that could see witnesses called to the Parliament.

Since March 25, police forces have required judicial approval before using the Regulation of Investigatory Powers Act (RIPA) to flush out a journalist’s confidential sources.

The RIPA allows police forces to access the ‘who, where and when’ of texts, phone calls and emails, rather than the content of the communications.

However, the IOCCO announced recently that two unnamed forces had flouted the new law and used RIPA in this way without judicial permission.

As revealed by the Sunday Herald, Police Scotland's Counter Corruption Unit is responsible for one of the two breaches referred to in the watchdog’s report.

Sir Stephen House refused to comment about the breach at the latest Scottish Police Authority meeting, while Justice Secretary Michael Matheson offered few details to MSPs last week.

“The Interception of Communications Commissioner’s Office — IOCCO — has made clear that it would be inappropriate for it to identify the forces under investigation while its investigation is on-going, and it has set out clear reasoning for that position.

“In light of that investigation, it would not be appropriate to comment further, other than to say that ministers expect all public authorities to comply with the code of practice on accessing communications data.”

However, the revelations have concerned human rights organisations, the National Union Journalists and opposition MSPs.

Holyrood’s Justice Committee convener, the SNP's Christine Grahame, has now written to the IOCCO about the watchdog’s continuing probe into the breach:

“You will appreciate that the Committee has a strong interest in these matters, inasmuch as there may be a Scottish element to them.

“The Committee would be very grateful if you could advise us of the relevant timescales for the investigation, including the likely date of the investigations being concluded and their findings being made public.”

John Finnie, another MSP on the committee, said: “We are seeking clarity from the IOCCO about their enquiries. If we decide to have our own inquiry, there will be witnesses.”

It is understood Police Scotland may be preparing to say that the breach did not relate to a journalist’s communications data.

However, the new regulations apply to attempts to identify journalists’ sources.

In the IOCCO report that flagged up the breaches, the Commissioner stated: “In the second case a police force acquired communications data relating to a suspected journalistic source working within the police force and a former employee of the force suspected to be acting as an intermediary.

“No data was acquired relating to the journalists who published subsequently an article which allegedly relied on leaked information from the police employee.”

The Sunday Mail newspaper reported recently that the breach could relate to its April investigation into the unsolved murder of Emma Caldwell.

Scottish Liberal Democrat justice spokesperson Alison McInnes MSP said: “The spying claims continue to hang over the force. The refusal of Police Scotland and the Scottish Government to confirm or deny Police Scotland’s involvement in this matter has only fuelled concerns about a conspiracy of silence. It’s important we get to the bottom of this and I look forward to the Commissioner’s response.”