The price of decarbonising Elgin’s Procurator Fiscal office has risen to £3.5 million.

The move will save £3,885 annually – meaning it will take more than 900 years for the cost to be reimbursed.

“This Crown Office scheme involves utterly ludicrous expense to the taxpayer for minute benefit,” former SNP minister Fergus Ewing told the Sunday Mail.

He added: “The annual savings will only be £3,885 and, as the total costs of the work are £3.5 million, it will take nearly 1,000 years to recoup the benefits. And that may not even take account of electricity running costs.”

The costs were originally set at £2.2m but rose to £3.5m within a few months.

The scheme was intended to show how Victorian buildings could be made environmentally friendly. But data revealed in a freedom of information request show that the project costs £2,342 per square metre. The gas bill of the building, however, is around £2,500. A 100-square-metre flat would cost £234,000 to convert.

The average cost of a Scottish home is £189,000.

A Crown Office spokesman said: “This investment will allow [the Crown Office] to meet targets to reduce carbon emissions by 2.5 per cent each year, become carbon neutral by 2040 and to help deliver Scotland’s transition to net zero.

“All contracts are subject to a robust and compliant procurement process to ensure maximum value for money.”