Council leaders claim the system is 'flawed' following the news that Salford was dropped from being rated as a 'Fair' to a 'Weak' authority just days before the nationwide scores go public.
With just days to go before the public announcement of scores, Salford was told that a late re-grading had dropped the authority's score, so that it is now categorised as a 'Weak' authority.
That's despite the fact that the city's education service has been judged to be doing well, having received a three out of four star rating, while Salford's social services has just achieved a two stars out of three star rating from the social services inspectorate.
The CPA inspectors have also endorsed a complete turnaround in the city's benefits service by awarding it a top four star rating. This compares to a one star rating for the same service just 12 months ago.
The city council is already among some of the top performing authorities in the country thanks to improvements to street cleansing and refuse collection.
Environment chiefs reckon their plans to introduce a kerbside collection scheme across the city over the next 12 months will also help register high marks with inspectors in future.
Bill Hinds, leader of Salford City Council, said that the judgement results of the downgrading could be 'devastating' for Salford.
'Since October we have been led to believe that our rating would be 'Fair'. All the indications we received from the inspection team told us the same thing. But at the last minute, through some kind of administrative sleight of hand, we have become rated as a 'Weak' authority.
'We can't appeal against that judgement now - in fact, we don't even know exactly why we have received this last minute judgement that skews our performance score so dramatically. The Audit Commission themselves say they can't tell us until after the new year.
'One of the areas we have been marked down on is our housing strategy. This has consistently been rated as a strong point in Salford, and government have always said that we are above average with no weaknesses for housing strategy in each of the last four years.
'Now, without any warning or explanation, we are suddenly judged as poor at housing strategy and that has brought about this late change in our overall rating. To have dropped in this way is inconceivable. I cannot believe that the scoring can have changed so dramatically at the 11th hour.
'We have taken legal advice and believe we have sufficient grounds for a judicial review.
'We don't believe we are a weak authority, and the inspectors who actually came to Salford said they don't feel we are a weak authority. We believe we have been penalised as a result of some kind of paper exercise. The result is that this rating does not take into account the major pioneering work this authority has consistently achieved.'
The comprehensive performance assessment report, and the city council's proposed improvement plan, are available on the city council's website.