One of the oldest swimming baths in Lancashire is set to close for major repairs that will extend its life by another 20 years.

Brinscall Swimming Pool in Chorley will shut its doors for six months to allow a £600,000 overhaul to be carried out after borough councillors were told that the pool structure could fail “catastrophically” if remedial action was not taken.

The popular village facility was built in 1911, but was recently deemed to be “well past its design life” by a structural engineer who noted that fixes put in place over the past 12 years were themselves now beginning to fail.

Although the overall structure of the building is understood to be sound, there have been growing concerns about the condition of the concrete floor of the pool and its steel reinforcement.

The pool has been subject to regular monitoring since a structural assessment carried out last October uncovered “significant defects” as a result of corrosion.

A recent follow-up visit found that the problems are worsening, with cracking visible in the pool’s retaining walls and the surrounding walkway.

Chorley Council was presented with three options for the repairs now needed to keep the historic baths afloat – ranging from additional “propping” of the pool floor, which would enable the facility to remain open for up to three years, through to a £1.2m wholesale structural renovation, which would see it through until the 2070s.

However, deputy council leader Peter Wilson told a cabinet meeting that there was a balance to be struck between preserving the pool for the foreseeable future and making a big splash investment – especially when other leisure sites in the borough were also “in desperate need” of refurbishment.

For that reason, the authority has opted for a renovation which will see all necessary repairs carried out, with the work expected to keep the baths in good condition for another two decades.

Council leader Alistair Bradley said: “Who knows where we’ll be in 20 years regarding this kind of facility. It may well be one of the last… of its type left the way that they’re going elsewhere.”

Cabinet members gave the go ahead to start the process of searching for a contractor for the job, but a date for the temporary closure has not yet been finalised. The authority is investigating whether swimming capacity can be increased at the All Seasons Leisure Centre, near Chorley town centre, for the duration of the shutdown.

Brinscall baths was gifted to the village by Victorian mill owners and entrepreneurs, the Park family.

Chorley North East ward councillor Margaret France said that she believed modern-day users of the pool – who include those from beyond the borders of the village – would be “understanding” of the closure and “grateful” for the work.

She added: ”I think it will be money well spent, because if you look at Brinscall and WithneImage: Specialist UK Restorations, via Chorley Council websitell, we don’t have a community centre, we don’t really have any other publicly-owned building other than Brinscall baths – and it’s extremely well used by a lot of school groups and various different organisations.”

But Cllr France also appealed for the changing rooms not to be made unrecognisable during the upgrade.

“The fact that they are so dated is part of the charm,” she said.

Euxton ward councillor Danny Gee questioned whether the “unique” nature of the facility would make it eligible for grant money from the lottery or other funding sources.

Cllr Bradley pledged that the authority would investigate the possibility, but Cllr Wilson cautioned that the council would likely be considered to be liable for basic maintenance so long as the baths remained in operation.