Victoria’s local government watchdog has closed an investigation into whether Melbourne Lord Mayor Robert Doyle and his team breached electoral donation laws despite uncovering potential breaches of the Local Government Act.

The 17-month investigation followed Fairfax Media revelations last year that the election campaign donation declaration made by the Doyle team contained apparently incorrect information.

The newspaper investigation found two hidden links to Chinese-born developer Jeff Xu, prompting concerns about transparency and possible conflicts of interest.

But this week acting chief municipal inspector Ross Millard said the inspectorate had been given advice that a successful prosecution of the Doyle team was “unlikely”.

That is in spite of a prima facie case and “evidence of poor practice” being established by the Local Government Investigations and Compliance Inspectorate.

“Members of Team Doyle have been reminded of their responsibilities and obligations under the Local Government Act in relation to campaign donation returns,” Mr Millard said.

The Age asked to see the legal advice provided to the inspectorate. A spokesman said the government watchdog adhered to the Office of Public Prosecutions guidelines and provided a link to 42 different policies.

Macquarie local government lawyer Terry Bramham said the reasons for not pursuing the case should be open to public scrutiny.

“The advice may be quite sound, but right now we don’t know what was discovered in the investigation and we don’t know the basis on what the advice was provided,” the said.

In July last year, the Doyle team self-reported three discrepancies in their election donation return – amounting to a previously undisclosed $19,500.

On Friday Cr Doyle said he regretted the omissions, but they were honest mistakes.

“After more than a year of investigation, I am personally pleased that this matter is now closed,” he said. “I have always been confident on the basis of legal advice to me, that there was no breach of the Local Government Act.”

The findings come as Melbourne City Council launched a conflict of interest register, for the first time providing a permanent log of councillors who are forced to dismiss themselves from voting on council matters over gifts and cash received.

In the first 20 months of their term, individual members of the five-person Doyle team have been forced 18 times to declare of conflicts of interest over money received through election donations. Cr Ken Ong has faced a conflict of interest five times over election donations and the two Greens councillors have made one declaration each.