Council finance bosses facing a budget shortfall of more than £3m have been criticised by inspectors.
The Audit Commission has branded financial management at Northampton Borough Council "poor" because it lacks leadership and has limited expertise.
The report accuses politicians of "undermining" improvements to services called "among the worst in Britain".
Leader Tim Hadland calls for a "massive turnaround" and the opposition said electors would judge performance next.
The Audit Commission report said: "Northampton Borough Council has made little progress since 2004 and has deteriorated in some key areas such as planning.
"Its weakest services continue to be among the worst in the country and weak political leadership is undermining improvement.
"Managerial leadership is inadequate and there is no stable and cohesive senior team.
"A vision is beginning to take shape and priorities are emerging but it has not yet been agreed with key partners.
"New finance systems have not yet been put into place to monitor spending accurately and the council has no clear picture of the likely out turn for the current year."