Calls have been made for further investigations into the extent of alleged bribery and corruption at Liverpool City Council.
Director at auditor Grant Thornton, Andrew Smith, said a forensic inquiry was required following the arrest of former mayor Joe Anderson.
A Best Value inspection report has been completed but focused on regeneration, highways, planning, and property and asset management.
Speaking at a meeting of Liverpool's audit committee this week, Mr Smith said he had been trying to obtain ‘evidence the alleged bribery and corruption issues do not go wider than is currently known' but that ‘our view is the evidence which management is presenting to us is insufficient'.
He added: ‘It's likely in our view that an independent inquiry is probably needed.'
Mr Smith said such an investigation should examine emails and text messages of senior officers from heads of department upwards, and interview key people.
However, Liverpool's chief executive Tony Reeves questioned whether such an investigation would be proportionate, as it would involve examining ‘hundreds of thousands of transactions'.
He added: ‘We are concerned about how you prove a negative and the cost of doing so.'
Director of finance and resources, Mel Creighton, warned of the impact on the cost of borrowing should the auditor issue a qualified opinion.
Further meetings between the auditor, management and commissioners will take place in the next few weeks.
Mr Smith said he was unable to give a ‘clear indication' of when the 2019-20 and 2020-21 audits would be signed off.