Bath's £20m spa project has been a stop-start affair since the original project was unveiled in September 2000.
The spa building is still shrouded in scaffolding
An NHS spa treatment centre on the site was closed on health grounds in 1978 and since then, attempts to restore the spas have failed because of cost and concerns over the purity of the water's source.
But in 2000, the Millennium Commission gave a grant of £7.78m to refurbish five listed buildings within the complex, including the 18th Century Hot Bath and Cross Bath.
Work on the ambitious project began soon afterwards but the scheme was plagued by a series of delays culminating in a further setback on 7 May.
Chris Cavanagh, of Bath and North Somerset Council (BaNES) said: "A commitment has now been made to complete the building works by the end of June.
"We are continuing to work together with Mowlem and Thermae Bath Spa to complete and open this exciting project at the earliest possible date after that.
It's going to be longer and longer before any money comes in from visitors and users of the spa, so it's costing us a penny or two
Peter Rollins, Bath Spa project
"There is an added incentive of completing and opening the new spa to tie in with the Pavarotti concert on 7 August."
Hoteliers in the city say they have been affected by the delays with a loss of potential bookings.
One said: "When we have inquiries, we are having to temper our response with 'Well, we know it's opening soon', but we can't take a firm booking on the strength of its opening and that's a bit disappointing."
Peter Rollins of the Bath Spa Project said: "This is both disappointing and frustrating for everyone involved.
"It's going to be longer and longer before any money comes in from visitors and users of the spa, so it's costing us a penny or two."
Richard Hall of Bath's Chamber of Commerce said: "Delays are clearly disappointing - this was supposed to be a millennium project.
"But when it is open it will trigger lots of new projects around it, contributing towards a rebirth of spa culture in this country."
When it opens, the scheme's centrepiece will be a new building on the site of the old swimming baths featuring multi-level pools, treatment and steam rooms, massage jets and rest areas.