Anas Sarwar has described an allegation that a former Scottish Labour MSP hid a secret camera in a Holyrood toilet as “deeply distressing and shocking”.

Colin Smyth, 52, is facing a criminal charge over the claim, which he denies.

The South Scotland MSP, who has been suspended by Labour, was also charged separately last month over possession of indecent images of children.

He is due to appear at Dumfries Sheriff Court at a later date.

On Monday evening, the Scottish Parliament confirmed Smyth had resigned as convenor of the economy and fair work committee.

Speaking at a news conference in Glasgow, Sarwar described the allegations against Smyth as “deeply distressing and shocking for all of us and for people across the parliamentary estate”.

The Scottish Labour leader said he had had not been aware of any concerns about Smyth’s behaviour prior to his arrest, but that Labour suspended him as soon as it knew of the “seriousness of the allegations”.

Sarwar told reporters he would “like to believe” the toilets in the Scottish Parliament were safe, adding that “everyone deserves that basic dignity”.

However, he said that was a question for Holyrood officials.

Smyth, now an independent MSP, has held several frontbench roles with Scottish Labour and was previously the party’s general secretary.

The economy and fair work committee will select a new convenor to replace him on Wednesday.

Earlier, First Minister John Swinney said he was “horrified” by the allegations against Smyth.

He added: “I know that parliament will be working very hard to reassure individuals who will be deeply concerned as I am.”

Holyrood party leaders are due to meet with the parliament’s presiding officer and chief executive on Tuesday.

The Sunday Mail has reported at least five MSPs, one journalist and several staff members have been contacted by police over alleged secret toilet recordings at Holyrood.

Smyth was charged over possession of indecent images following a search of his home in Dumfries on 5 August.

The news did not become public until 20 August, when it was reported in the Daily Record.

The MSP said at the time that he was “fully co-operating” with the investigation.

Smyth’s parliamentary pass was revoked last Thursday, on the same day it was reported that he allegedly hid a secret camera in a Holyrood toilet.

He denied that allegation and criticised Police Scotland for releasing details of its investigation.

The Scottish Parliament confirmed that police had searched all toilets and changing rooms but found no “covert recording devices”.

Smyth – a former modern studies teacher who has a wife and two daughters – could potentially contribute to debates and vote remotely when parliament returns from recess this week, though BBC Scotland News understands that he has been signed off from work on medical grounds.

It is understood that Scottish Labour became aware of of serious allegations on 18 August and suspended him on that day.

The Scottish Parliament said it was told on 8 August that police were investigating images potentially taken at Holyrood, but that officers did not say who their inquiry related to. The parliament said on Monday that this was still the case.

The parliament said it became aware that Smyth had been charged over possession of indecent images of children when it was reported in the media on 20 August.

The Scottish Parliament Corporate Body did not suspend his pass until eight days later.

The suspension was made on the basis of the indecent images charge following “recommendations from officials”, according to a Holyrood spokesperson.

They added: “Its decision was based on a full risk assessment and the balancing of a range of duties and responsibilities placed on it.”

• 5 August: Colin Smyth arrested and charged over possession of indecent images of children.
• 8 August: Police tell parliament about an inquiry into images potentially taken at Holyrood. However, officials are not told who officers are investigating.
• 18 August: Labour becomes aware of serious allegations against Smyth and suspends him. It is understood parliament is also told.
• 20 August: Smyth’s suspension becomes public. Police confirm the charge over indecent images.
• 28 August: Smyth’s pass is revoked (officials later say that decision was based solely on the indecent images charge). The same day, the Daily Record reports Smyth is also facing a separate charge over the hidden camera allegation.
• 29 August: Parliament says no covert devices were found in a search and that it is supporting staff.
• 31 August: The Sunday Mail reports at least five MSPs, one journalist and several staff members have been contacted by police over alleged secret toilet recordings in parliament.
• 1 September: Parliament says it still does not know for a fact that the police investigation into images potentially taken at Holyrood relates to Smyth.

This whole story, and the associated fall out, has rocked those based at Holyrood.

It’s shocking enough that a long-serving MSP is facing such serious charges.

But the allegation that a secret camera may have been placed in the Holyrood toilets has stunned those who work in the parliament.

This goes beyond a parliamentarian facing serious allegations. It’s that many building users are questioning if they’ve been caught up in all of this.

Scottish Parliament officials have been at pains to reassure Holyrood pass holders that they’re taking their safety incredibly seriously.

But there’s a still a sense of disbelief.