The project, being carried out with the aid of a£8m lottery grant, has been blighted by delays and a series of public falling outs between Bath & North East Somerset Council and site contractors, Mowlem Plc.
Lord Justice Mance said any further delays would cause 'unquantifiable' damage to the local economy and public confidence and would threaten to reduce the spa 'from the status of 'Eden' to 'Dome''.
Mowlem came away with nothing from the case - except an order that it must pay the council's£22,500 legal costs bills.
The injunction was first granted by a judge in October last year who said council contractors should be given access to the site so that they can blast off the offending paintwork.
He did so despite fierce objections from Mowlem who insist they are in no way to blame for the state of the paint covering the historic site's four state-of-the-art new pools.
But, upholding the injunction, Lord Justice Mance said the alternative would be 'unquantifiable' losses for Bath & North East Somerset Council.
He said any further delays in the project would probably cause 'further loss that would be felt by the general public'. Local hotels, restaurants and other businesses who hoped for a bonanza when the baths opened are already feeling the pinch.
And the judge, sitting with Lord Justice Brooke and Mr Justice Park, said more delay would have an impact on public confidence in the council and have 'negative implications' for other projects.
'These items represent the type of unquantifiable, and in substantial measure, irrecoverable damage to public interests that m ay well be suffered if a Millennium project undertaken by a public authority moves from the status of 'Eden' to 'Dome'', he told the court.
The council was 'entitled to evaluate the course most favour to it', said the judge, and Mowlem will now have to allow other contractors onto the site to remove the offending paintwork so that any defects in the concrete beneath can be revealed to all.
Mowlem has always insisted the real problem lies with the paint itself which it was told to use in the project specifications. It says that removing the paintwork will show once and for all that it is not at fault.
The£26m project was approaching completion before the dispute erupted, but the injunction means that fixtures - including underwater ghting and water jets - will have to be taken out so that the paint can be stripped from the walls.
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