Mackerel has been struck off a list of sustainable fish as conversationists warn that overfishing is leading to depleting stocks.

The oily fish once championed by celebrity chefs as a healthy and ethical option should now only be eaten occasionally and where possible from local sources, according to The Marine Conservation Society (MCS).

The conservation group has removed mackerel from its "fish to eat" list, recommending herring and sardine as alternatives.

Mackerel populations in the Atlantic have shifted northwest towards Iceland and the Faroe Islands, where they are being heavily fished, experts explained.

"The stock has moved into Icelandic and Faroese waters, probably following their prey of small fish, crustaceans and squid," said Bernadette Clarke, fisheries officer at the MCS.

"As a result, both countries have begun to fish more mackerel than was previously agreed.

"The total catch is now far in excess of what has been scientifically recommended and previously agreed upon by all participating countries."

Celebrity chef Hugh Fearnley-Whittingstall, whose "Fish Fight" campaign aims to change the laws on fishing quotas, has been forced to drop his support for eating mackerel following the guidance, the Daily Mail reported.

Jamie Oliver, Raymond Blanc and Gordon Ramsey have also previously hailed the oft-overlooked brown-fleshed fish, which is rich in Omega 3, as a healthy and affordable culinary choice.

Along with mackerel, gunard has also been taken off the list because of concerns about population levels of the fish, which is traditionally swept up by vessels fishing for other species and is often thrown back into the sea.

Herring, coley and Dover sole from the English Channel, on the other hand, can be eaten with a clear conscience, while whiting from the Celtic Sea off the south coast of Ireland is given the green light for the first time.