Portsmouth City Council's resources decision-making meeting heard campaigner Mark Austin play a section of a recording which he told councillors was of a leading council officer.
It heard a man on the tape speaking out against Michael Lawther, the city solicitor, and Julian Lomas, the former director of environment and transport.
Councillors heard the man on the recording talk about a woman called Wendy.
As reported in The News, a police probe was launched last year after Wendy Couch, then a council employee, was found to have failed to declare gifts, including an overnight stay on a yacht, from the company behind the Northern Quarter scheme, Centros.
Police decided that although she had broken council rules, she had not committed any criminal offence.
Ms Couch has since left the council.
Mr Austin, a vocal opponent of the council's Northern Quarter plans, told councillors: 'This is a leading council officer.
'This concerns me,' before playing the recording to the meeting at the council's civic offices on Thursday.
The extract, which was an edited version of a longer recording, said: 'He is a conman, Lawther is a conman. Lomas said let's look after Wendy, and Lawther said leave it to me.
'It was a cover-up.'
Mr Austin told the meeting: 'These are serious allegations.'
After the meeting he said: 'I feel I have had no choice but to release this tape because of the way the council have dealt with my concerns.' The tape has been passed to the police and the district auditor for investigation.
David Williams, the chief executive of Portsmouth City Council, said he had every confidence in Mr Lawther and his work.
He added: 'We have been given a copy of a recording made by Mr Austin which appears to be of conversations he had with a member of staff.
'I have provided a copy of the recording to the police and the district auditor to establish whether it contains anything new or of interest to them and their previous enquiries, none of which found any evidence of criminal wrongdoing.
'I will take appropriate disciplinary action if any is needed.
'The council does not comment on individual employment issues, as staff have a right to privacy.'
Mr Lawther declined to comment and The News was unable to contact Mr Lomas.
alex.forsyth@thenews.co.uk