A historic outdoor swimming pool in Bath could be re-opened in three years' time.

The Cleveland Baths have been closed for 25 years and were put on the national buildings at-risk register by government body English Heritage in 2007 where the complex has remained for two years.

This week the 19th-century lido was placed on the most serious category on the list, which means there is an immediate risk of further rapid deterioration or loss of fabric.

The pools are owned by Bath and North East Somerset Council which is in negotiations with a group of developers and charities looking to bring them back to use for bathers.

The Cleveland Pools Alliance includes Prince Charles's Prince's Regeneration Trust, the Trevor Osborne Property Group and the Cleveland Pools Trust.

The alliance is working through details of a lease with B&NES Council, as well as planning applications and fundraising ideas, before work is put out to tender and the project can begin.

The baths were vandalised in September last year and yobs have again recently struck at the Grade II-listed site by scarring it with graffiti.

Cleveland Pools trustee Ann Dunlop said: "The Cleveland Pools Alliance representatives meet from time to time but things move incredibly slowly when the council and lawyers are involved.

"There has been slippage so I believe that it will be at least the summer of 2012 before we can put on our swimsuits."

The alliance is hoping to secure permission to open the pools for the national Heritage Open Days celebration in September. The group will use the day to raise awareness and recruit more trustees.

It has also applied for an English Heritage grant to help fund a feasibility study of the project.

Osborne Group founder Trevor Osborne said it was important that plans for the future of Cleveland Baths also included accommodation for security officers so the site could always be supervised.

He said: "It is a lovely pool and it would be wonderful for Bath to see it restored."

Prince's Regeneration Trust chief executive Ros Kerslake said: "It's absolutely critical that we are able to progress quickly with the alliance's acquisition of the pools, so that we can begin work on bringing these wonderful facilities back into community use before they deteriorate any further.

"This requires the active support of people locally, and in particular, of the council."

English Heritage also again included the 18th-century King Edward's School in Broad Street on its list of historic buildings at risk.

It described the privately-owned site as being in a 'fair' condition after the completion of roof repairs.

English Heritage says more than one in 11 conservation areas in the South West are at risk of neglect, decay or damaging change – including those at Bathampton and Batheaston – and is now launching a Conservation Areas at Risk campaign to get residents, local groups and councils working together to improve them.

The Bath Preservation Trust said the inclusion of the two villages was an argument for the refusal of plans for a park and ride scheme at Bathampton Meadows.