Croft School cost about £800,000 more than originally hoped – and Swindon Council is blaming the situation on money earmarked for highways works in the area.

The controversial school, next to Croft Sports Centre, off Marlborough Lane, was originally planned to cost £4.5m, but the Adver can reveal the total price tag for the project has ended up as £5,293,501.

On top of a main budget of £4.5m, the council also budgeted a contingency of £500,000, which it used to cover an estimated £500,000 of unexpected highways mitigation works which were agreed by the planning committee.

Residents say the only roadworks so far have been to improve a short stretch of Marlborough Lane, even though only £100,000 of this cash was originally supposed to be saved for work arising after the school was opened.

During construction, the council spent another £400,000 on abnormals, which include £124,000 on sheet piling to retain part of the site, £118,000 on piling mats due to poor ground and £78,500 on excavations associated with site levels.

It means the final cost of constructing the school was £4,793,501, not including the £500,000 for unexpected highways works or the budgeted contingency used to offset it, making a total overspend of £293,501.71 on the £4.5m budget.

When asked to explain the overspend in a Freedom of Information inquiry, Swindon Council responded: “The budget has had to cover an unexpected £500,000 of highway works generated by the planning permission conditions. If this was not the case the budget spent, including a standard level of contingency, would be under budget.”

Croft School is the first to be built under the council’s own modular Class Solutions design, which the council is trying to sell to other authorities on the basis it is one third cheaper to build than a traditional school, quicker to construct and cheaper to run and maintain.

Swindon Council says Croft was still far cheaper to build than a standard primary school of the same size. Millbrook cost £6,562,365 and Oakhurst cost £6,874,364.

Colin Doubleday, the chairman of Pipers Area Residents’ Association, said: “It is hard to comment specifically on the costs of one specific school in isolation. “It would be very interesting to see the comparable costs of building the brick-constructed school at Wichelstowe which was finished a year before. “We are also interested to know if these costs include the substantial ground works to stabilise this very wet ground and the noise fences and landscaping that have still not been completed.

“The important thing is that the school is now here and has 50 pupils. Over the next few years it is planned that there will be 420 pupils, that is 1,680 journeys a day. “The council promised to spend up to £500,000 additional contingency budget on roads and we understand initial consultations are to start shortly about how this traffic could be managed.”

Coun Brian Mattock (Con, Old Town), who is also the deputy council leader, said: “I’m never happy if we don’t get anything achieved on target, but as far as value for money is concerned that figure is very much less than the £6.5m cost we’ve had in the past.”

He said some of the highways money was still available and councillors were talking to the community to determine how the rest should be spent to benefit the area.