Conservationists say stocks of the chip shop staple in some areas are now unsustainable.
They include the North Sea, where the fish has been removed from the Marine Conservation Society's green list of recommended fish to eat after concerns over stock levels.
Fisheries further north around the Arctic and Iceland are still at sustainable levels, according to the MCS.
It wants customers to request so-called 'green-listed' fish in takeaways and restaurants.
Haddock has largely taken over from cod in the nation's signature dish.
The conservation group publishes a list of fish to avoid. It includes sea bass, bream and razor clams. It claims that 90pc of the world's fish stocks are over-exploited.
'The future of the fish supper is no longer guaranteed,' it says.
'Many fish stocks are in a state of serious decline, with over-fishing a great threat to marine wildlife and habitats.'
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