The industry revived to some extent during the 1950s; the British distant-water catch peaked in 1956 at 8.5 million tons. However, a period of gradual decline followed. Increasingly, the problems of distant-water trawling centred on limited access due to claims of territorial rights. The British distant-water fishing industry was based on the idea of freedom of the high seas, and the assumption that the sea was an open resource to be exploited. This idea was increasingly challenged in the post-war period.
During the 1930s, the Norwegian government had claimed a four-mile territorial limit and, after the Second World War, these limits were enforced. When the Norwegians arrested a number of British trawlers, the British government took the case before the International Court of Justice. The court found in favour of the Norwegians, who had argued for the primacy of local interests.
The Icelandic government had long-standing concerns about the depletion of fish stocks along its coast. Following independence from Denmark in 1944, Iceland annulled the Anglo-Danish Territorial Waters Agreement of 1901, which was due to expire in 1951. This treaty had mutually restricted territorial waters to within three miles of the coast, but now the Icelandic government extended the limit to four miles. The case was put before the International Court of Justice. The British industry banned Icelandic vessels from landing fish in Britain. These events led to a long-running dispute between the British and Icelandic fishing industries and governments.
Britain was forced to concede the four-mile limit following a decision by the Organisation of European Economic Co-operation in 1956. In 1958, however, the United Nations (UN) held the first International Conference on the Law of the Sea. Various nations made claims for extending the limit of territorial waters to 12 miles, but nothing definite was decided. The Icelandic government unilaterally declared a 12-mile limit.
Britain did not recognise the Icelandic declaration and continued to fish within the new limit. This led to the first Cod War, in which Iceland's Navy harassed British trawlers. There was some violence, including 'rammings', and Royal Navy ships were deployed to protect the trawlers. Following the United Nations Conference on the Law of the Sea between 1960 and 1961, Britain agreed to the 12-mile limit.
In 1970, the European Economic Community (EEC) drew up a Common Fisheries Policy, which allowed equal access to community waters by all community members after ten years. The industry considered that this was against their interests, but the Prime Minister, Edward Heath, was determined that this would not prevent Britain from joining.
In September 1972, however, Iceland declared a 50-mile limit. The outcome was the second Cod War, in which Icelanders used 'cutters' to sabotage the nets of British and German trawlers. The dispute assumed greater international significance because of American anxieties about the US/NATO base at Keflavik in Iceland, and the possibility of an Icelandic rapprochement with the USSR. In October 1973, UK and Icelandic representatives agreed that a limited number of British trawlers would be allowed to operate within the 12-limit for the following two years.
In 1975, at a third United Nations (UN) Conference of the Law on the Sea, it became apparent many countries supported a 100-mile limit. In May 1975, Iceland declared a 200-mile limit. The British government refused to recognise this, which led to the third Cod War. By the end of 1976, the British conceded the limit. The closure of the Icelandic grounds effectively ended British long-distance fishing.