Offshore workers will refuse to fly on Super Puma helicopters despite aviation authorities lifting their ban on them, unions say.

The aircraft were grounded in the wake of a fatal crash in Norway last year, which killed 13 people including Iain Stuart from Aberdeenshire.

It was the third fatal accident involving a Super Puma in the North Sea since 2009 and nine of out of ten oil workers say they are against their use.

The Civil Aviation Authority (CAA) last week cleared a path to allow them to return to service in the UK but unions say their members will refuse to fly.

"The only conclusion we can reach about the way this has been handled is that a commercial imperative exists and is taking precedence over appropriate engagement and consultation with... the offshore workforce," the Unite and RMT unions said in a joint statement.

"We fully support the principle of workforce engagement and we feel that Airbus and the regulators have fundamentally failed in this.

"We therefore find ourselves at odds with both Airbus and the regulators."

They said: "As we see it, there is only one way to remedy this situation and that is a comprehensive and meaningful engagement exercise of offshore workers."

"Until such an engagement exercise has been completed, the position of the TU's representing oil and gas workers will be that our members refuse to fly," they added.

John McColl, head of airworthiness at the CAA, said the decision had not been taken lightly.

"The safety of those who travel on offshore helicopter flights is a key priority for both the UK and Norwegian aviation authorities," he said.

Super Pumas will not return to duty immediately and it will be up to individual companies to decide whether they still want to use the aircraft, the CAA said.

If they do, more frequent inspections will have to be carried out and components must replaced sooner. Airbus will also have to partly redesign the helicopter.

CHC has already stopped using Super Pumas, citing a "lack of commercial demand", and BP has said it will not use them until the inquiry into the latest crash is complete.

The cause of the accident off Norway in April 2016 is still unclear but experts believe it was the result of a technical fault.