THE cost of the M4 relief road around Newport will cost more than £2.3 billion - according to environmental campaigners.

The Welsh Government’s latest consultation on the M4 Newport bypass puts the cost of the project at £1.1 billion but environment group, Friends of the Earth, say the cost of the project will be double that, accusing the government of neglecting to include VAT, inflation or maintenance and repair.

A detailed report into the plans was released last week, showing the scheme would cost a predicted £1.093 billion and be complete by autumn 2021. This was despite the first minister Carwyn Jones claiming in November 2015 that the final figure would be “well below” £1 billion.

Gareth Clubb, director of Friends of the Earth Cymru, said: “If any of us want to make an extension on our house we need to know how much it’s going to cost. We can’t possibly exclude things like VAT and maintenance. But the Welsh Government is sweeping these massive costs for the M4 under the carpet and hoping we’ll all forget about it.

“We’ve calculated that the scheme will cost more than £2.3 billion once VAT, inflation and maintenance is included."

He added: “This makes a huge difference to the cost-benefit analysis too. If the cost is doubled then we end up with a scheme that provides less benefit than it costs We’d be better off stuffing £2 billion under the mattress than spending it on the M4."

They have calculated the total of £2.332 billion from the published cost of the scheme £1.093 billion, with £0.175 billion they have calculated for inflation (construction inflation is roughly 5 per cent per year), plus maintenance of £0.675 billion (based on 2013 Welsh Government figures plus 10 per cent to account for 10 additional bridges plus inflation), along with £0.389 billion for VAT (currently at 20 per cent).

The plans would see a new 23km stretch of road running south of Newport built between junctions 23 and 29 of the M4. According to last week’s report it will involve building 35 new bridges and knocking down 12 residential buildings – including the Grade II listed Vicarage in Magor.

If the scheme goes to plan, work will begin in spring 2018, with the new section of motorway to open in autumn 2021 and the existing stretch of the M4 to be reclassified as a trunk road 12 months later.

Mr Clubb added: “The Welsh Government needs to come clean on the total cost of this environmentally devastating scheme. As it stands the Welsh Government is deceiving the people of Wales.”

A Welsh Government spokesman said: “The most recent Economic Assessment examines all costs robustly and fairly, and shows that the project would not only inject nearly £1bn into the local economy, it would deliver £2bn of benefits to commuters and around a further £1bn to the wider Welsh economy. People should be in no doubt about the absolute importance of this project to the Welsh economy, as echoed by the CBI and 60 business leaders only last month.

"We remain committed to delivering this vital infrastructure investment at the best value for money. A judicial review has already ruled in our favour against Friends of the Earth that we properly assessed alternatives before deciding the preferred route.”