Whakatane Mayor Tony Bonne's election over-spending is now under police investigation as the number of complaints over his campaign costs rises to four.

A five-page detailed complaint by unsuccessful mayoral contender Ian Shearer comprises the latest assault on Mr Bonne's credibility following the mayor's admission that he over-spent during his campaign.

Dr Shearer, who called Mr Bonne "a cheat" after the mayor admitted over-spending the $20,000 legal limit by $928, alleges Mr Bonne over-spent by more than he has declared.

He has called on the police to "accurately determine such expenditure and to determine whether any or all" of his allegations are valid.

Dr Shearer, who has lodged the complaint on behalf of Community Focus, a rural communities group that supported him during the election, lists six areas he believes warrant close investigation.

The first involved Mr Bonne's use of an MCC Smartcar, loaned to him by a friend for the campaign.

He said Mr Bonne could not write off the cost of the benefit he obtained from the distinctive Smartcar, or its running costs, under a clause exempting personal vehicle running expenses.

Mr Bonne already owned a four-wheel drive vehicle for his personal use, he said.

The equivalent rental cost for a vehicle for up to eight weeks -- less $1000, the maximum an individual could donate to a campaign on an exempt basis -- should have been declared.

Dr Shearer also said the cost of the personalised plate BONNE, fixed to the Smartcar during the campaign, was not declared.

Eastern Bay police Area Commander Sandra Venables said this week she had appointed Detective Senior Sergeant Greg Standen to investigate the complaints.

Independent Election Services, which conducted the Whakatane mayoral election on October 9 that Mr Bonne won by more than 600 votes, this week confirmed four complaints had been lodged.

Mr Bonne blamed GST for his over-spend saying he did not realise the $20,000 limit was GST inclusive.

If the over-spend is ruled inadvertent, Mr Bonne faces a fine of up to $5000. If it is determined he concealed campaign expenditure, the penalty is up to two years in jail and a $10,000 fine.

Under the Local Government Act 2002, successful prosecution for the latter breach would rule him ineligible to serve as mayor.