New Zealand First leader Winston Peters said he had filed two privileges complaints against Prime Minister Bill English, claiming he has misled Parliament with his answers to questions about National MP Todd Barclay.
Mr Barclay yesterday announced he would not stand for Parliament again, after new media reports about a recording of a former staff member in the Gore electorate office.
Watch Bill English's media standup:
The former staff member, Glenys Dickson, laid a complaint with the police about Mr Barclay making a recording of her in the Gore office.
Mr English has had to defend his actions, after he spoke to the police as part of that investigation, and about his knowledge of a confidentiality agreement struck with Ms Dickson.
Mr Peters said Mr English had been making statements which were untrue and he should be held accountable.
"He was involved, as was the board of the National Party - and no doubt the ninth floor of the Beehive - in the cover up because there was Parliamentary, tax-payer's money used to get a confidentiality agreement with the person who had the information, who was the complainant.
Mr Peters said that confidentiality agreement was an illegal contract, because it sought to cover-up a crime.
Mr English allowed Mr Barclay to remain on as an MP and as a member of the National Party caucus after the incident.
He informed the electorate chairman about the recording and confidentiality agreement, and was then interviewed by police as part of the investigation.
Labour Party leader Andrew Little said Mr English's credibility has been undermined by standing back and letting Mr Barclay make untrue statements.
He said there had most definitely been a cover-up by the Prime Minister.
"There was a reasonably significant payout and it has been funded, at least in part, by the Prime Minister's office, which I would've thought was unusual."
Earlier today, Mr English said Mr Barclay's behaviour was not acceptable, in that it led to an employment dispute including with people he had previously worked with whom he considered competent, but that was resolved in the "correct" way.
However, he insisted he personally did not try to conceal anything, and left it in the hands of the police.
"I refute the allegations of cover-up," he said.
"The inference that nothing happened is wrong.
"There couldn't be a more serious process than the one that was initiated by a complaint to the police about the recording."
Mr English said the local electorate was responsible for reselecting Mr Barclay as the candidate last December, a process he had no formal role in.
"I couldn't be a voter or a delegate as part of it and came to the view that the former MP becoming involved in this selection, particularly one that was contested in this way would probably polarise it in a way that was worse."
And Mr English said he was not aware of any details about claims a National Party board approached a former electorate staff member of Mr Barclay's over a police complaint.
But he said it was not surprising a board member got in touch with Ms Dickson.
"If you have a bust up in an electorate, and this one was pretty spectacular, then it would be irresponsible for the National Board to pay no attention to that.
"Now just exactly what actions were taken I can't tell you."
'Conversations were private' - National Party
The National Party said members of the board, including Glenda Hughes, were in touch with party members in Clutha-Southland, but would not reveal any details about those conversations.
In a statement the party secretary, Greg Hamilton, said board members had various discussions with numerous party members in the electorate over several months.
But he said it would be inappropriate to discuss any details in the media.
"Those conversations were private and all discussions around the board table are conducted in confidence.
"I have absolute confidence Glenda would have acted with integrity at all times."
Yesterday, police said they were reassessing information discussed publicly in the last few days to see if it had any impact on the findings of the original inquiry into Mr Barclay.
They said they did not lay charges due to insufficient evidence but expected to make a decision early next week about whether to reopen their investigation.