The Scottish Parliament, which has transparency as one of its founding principles, has been censured by the country's information watchdog for excessive secrecy.

The ruling refers to the Scottish Parliament's Public Petitions Committee, established at the birth of the parliament to ensure citizens could take issues of concern direct to MSPs. It has been praised for encouraging public involvement in democracy.

Now, however, Scottish Information Commissioner Rosemary Agnew has ruled the Scottish Parliamentary Corporate Body (SPCB), the institution's governing body, has breached freedom of information laws after it declined a request from a whistleblower.

Rab Wilson, a former psychiatric nurse best known as the whistleblower who forced NHS Ayrshire and Arran to reveal hidden files on adverse healthcare incidents, wanted to know how many petitions had been submitted to the committee since its inception, and how many had been successful.

He also asked to know how long on average it took to process a petition and the number of petitioners satisfied with the outcome of their petition.

However the SPCB told him to find the information himself, saying it was in the public domain.

It also claimed it did not collate details of how many petitions had been submitted and what proportion were upheld or turned down.

It said details of whether petitioners were satisfied with the outcome were not held and would be subjective in any case.

When Mr Wilson appealed to the Information Commissioner, Ms Agnew agreed with the SPCB on the last point. But she said the SPCB "generally failed" to comply with the law in dealing with his request.

She said it had been unclear about the legal grounds on which it refused his requests, and had not clarified the "vital" distinction between petitions submitted and those subsequently considered by the committee.

In relation to what appeared a simple request for the number of petitions presented to the Scottish Parliament, the SPCB chose to consider only "admissible" petitions, not those submitted and subsequently rejected. More than 1500 have been lodged, given a number and published since 1999. But many more have been deemed inadmissible.

In her decision on the case to be published next week Ms Agnew instructs the SPCB to review Mr Wilson's request. She says if it continues to insist Mr Wilson could obtain the information himself, the SPCB should give him "reasonable directions' to where the information could be found.

The commissioner had given the parliament "a rocket", Mr Wilson said. "The five questions I asked were very straightforward, but the SPCB has been utterly evasive over the last six months," he said. "We need to know whether public petitions are upheld or turned down and whether people are getting results."

He added: "Every major company … takes customer satisfaction seriously. But the public petitions committee doesn't even gather this information."

A Scottish Parliament spokesman said: "We are pleased the Commissioner partly sided with the SPCB. We will reflect carefully on her full ruling and respond appropriately."