Mackerel has been taken off a list of sustainable fish to eat regularly, amid a fear of overfishing.
The removal by the MCS of mackerel from its list of "fish to eat" comes after the Marine Stewardship Council, which certifies fish stocks that are managed sustainably, suspended its certification of the north east Atlantic mackerel fishery.
Atlantic populations have moved north west into Icelandic and Faroe Islands waters, prompting their fishermen to fish more stock than was previously agreed and causing a dispute between the countries that target the fishery.
Mackerel has been a favourite fish for health-conscious Britons for a number of years.
Bernadette Clarke, fisheries officer at the MCS, said the stock has moved to follow its prey of small fish, crustaceans and squid.
"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 - negotiations to introduce new catch allowances have so far failed to reach agreement."
The conservation group said alternatives to mackerel included herring and sardine, and if people wanted to continue to buy mackerel, they should ensure it is as sustainable as possible - for example, fish caught locally using traditional methods.
TV chef and campaigner Hugh Fearnley-Whittingstall said "politics and greed are getting in the way of common sense" in managing the mackerel fishery.
On his River Cottage blog, he said: "If the countries involved could agree sensible catch limits this could still be a certified sustainable fishery.
"We hope that these so-called 'mackerel wars' can be laid to rest as soon as possible, so we can all go back to eating mackerel again with a clear conscience."
He also said the MCS had advised that handline-caught mackerel from inshore boats was the best choice to make when eating the fish.
Another fish taken off the "fish to eat" list is gurnard, because of a lack of data on population levels and concerns about how stocks of the increasingly popular fish are being managed.
Many gurnard which are caught are discarded, a wasteful practice which sees useable fish thrown back into the sea, because there is still relatively low demand for them, Ms Clarke added.
But the latest version of the "fish to eat" list also shows that herring stocks, coley and Dover sole from the English Channel are all good to eat with a clear conscience.
Whiting from the Celtic Sea also appears on the list for the first time.
Cod stocks from the North Sea are still below recommended levels, the MCS said, but a number of other popular wild fish are given the green light to appear on the dinner plate, including haddock and lemon sole.
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