The man who oversees complaints about politicians in Wales has resigned after he was secretly recorded by an assembly member.
Standards commissioner Sir Roderick Evans said "highly confidential conversations" with his staff had been taped.
The former Plaid Cymru AM Neil McEvoy has confirmed he made the recordings.
Police are being asked to investigate and the assembly has arranged a sweep of the organisation's estate.
The South Wales Central AM, who now sits as an independent, alleged he had found evidence that he claimed had brought Sir Roderick's office into disrepute.
He said he had acted lawfully and in the public interest. He had been facing three separate investigations by the standards commissioner at the time, before Sir Roderick resigned.
Sir Roderick, a former high court judge and pro-chancellor of Swansea University, said Mr McEvoy's actions were "wholly unacceptable" as he stood down on Monday.
"It has come to my attention that conversations with my staff about a variety of highly confidential and sensitive matters have been secretly, and possibly illegally, recorded over a period of what seems to be several months and in what seems to be a number of different locations by an assembly member," said Sir Roderick, who had served as the assembly's standards commissioner since 2017.
"These have included highly confidential conversations with my staff including references to cases brought by members of the public.
"That a member of our national assembly could behave in this way is wholly unacceptable. It undermines the integrity of the complaints procedure and brings our democratic process into disrepute.
"I'm not prepared to continue in my role as standards commissioner."
Welsh Assembly presiding officer Elin Jones said she had accepted Sir Roderick's resignation, and the process to find a successor will now begin.
She said: "Covert recording of private conversations is a serious matter and we will be asking South Wales Police to investigate how such recordings were obtained.
"Arrangements have been made for a sweep of the Senedd estate to locate any unauthorised electronic surveillance devices."
In response to Mr McEvoy, the standards commissioner's office said: "The appropriateness of covert recordings of private and confidential conversations will be considered by the relevant authorities in due course."
Sir Roderick was embroiled in a row last year after he said a video featuring a Labour AM's face superimposed on a woman in a low-cut top was not sexist.
Earlier in 2019 he was accused of double standards after he recommended a Plaid Cymru AM Leanne Wood be reprimanded for a swear word in a tweet.