Last November, it was revealed that the brand new £18m Dargavel Primary should have been able to accommodate 1,100 pupils, but due to an “error” by officials, the new building can only hold 548 pupils.

Then in February, the local authority announced that it now expected 1,500 children to need to use the school by 2033 and that would require a new building with capacity for around 800 pupils.

Dargavel Primary is part of the privately funded Dargavel Village project, a multi-million-pound development to build 4,000 new homes on the site of a former Royal Ordnance Factory by 2034.

BAE Systems paid for the new school as part of its Section 75 agreement with the council. However, because it has built the school to the specifications supplied to it by the council its obligations under the agreement are now discharged, leaving the authority to pick up the cost.

In the latest board paper for the council’s education committee, officers admit that they have not yet secured land, no design finalised, and no commercial tender issued for construction.

Setting out indicative costs, they warn that they will be “further developed” when those are secured, “taking cognisance of geotechnical, topographical and infrastructure information as site surveys are progressed; and as design considerations develop”, The Glasgow Times reports.

They also warn that the estimates “are subject to further construction cost inflation volatility in the period up to where a contractor is appointed”.

For the new Dargavel Primary School, the cost will be somewhere between £42m and £45m. Meanwhile, the cost of extending Park Mains High School to accommodate another 400 pupils will be between £27m and £30m.

The council said some of the housebuilders and others who worked on the development of the site should contribute towards the costs for the work on the secondary.

It said: “As previously advised the financial implications of the new build primary school and the extension to Park Mains HS will require to be incorporated into the council’s capital and revenue financial plans as the scale of works and proposed design develops.

“The planning terms for the Dargavel development include a requirement for the developer to make a capital contribution towards the costs of increased infrastructure for secondary education.

“The actual contribution will be subject to further discussion between the council and the developer.

“It is likely in the absence of any other external capital funding being secured that the council will require to fund the remaining capital costs through prudential borrowing. Based on the upper end of the range of capital costs outlined above, annual borrowing costs would be in the region of £4m.”

Meanwhile, the board paper and a note to parents reveal that the existing Dargavel Primary School will need to implement a P1 cap of 75 children from Aug 2024 and that a ballot will be held to decide who gets into the school.

Renfrewshire Council leader Iain Nicolson said: “It is important we get the right solution in place to continue to provide a high-quality education for young people in the area and engage with the parent councils and wider school community as these plans progress.

“It’s right we provide an outline of the current estimated building costs now to help everyone understand the scale of the challenge ahead while detailed costs are developed as design work is finalised and these will be brought forward for full consideration.”

Neil Bibby, the Labour MSP for West Scotland called on the Scottish Government to help the council with the cost: “The expected bill to fix this incompetence by Renfrewshire Council has now more than trebled.

“This will concern both parents and taxpayers who will be left to face the consequences.

“Clearly, this does not just affect one school but will have a knock-on impact across the authority.

“The Scottish Government must financially support the council to clear up this mess, to help secure solutions for Dargavel children and to ensure no other child in Renfrewshire loses out from the budget shortfall.

“The ongoing external review must also continue its work and ensure there is full accountability for this major failure.”