Peter Bradley, Labour's deputy leader on the council, said the new estimate took into account money spent on designated sales from 1989 onwards.
This is an increase from the £21.25m stated in the district auditor's report which only covered the period between 1987 and 1989.
The postponed BBC Panorama documentary last night attacked new aspects of the borough's alleged gerrymandering policy.
Meanwhile, The Times (p1) reports that according to objectors who instigated the original auditor's inquiry, at least another five councillors had been involved in malpractice.
The paper cites Mr Bradley as saying that the alleged malpractice had cost every local taxpayer £500.