At the time this was a very controversial decision. Few had grasped that European Law took precedence over UK law because Parliament had agreed that this should be so. This issues was to be revisited in the Brexit litigation.

The background

There was pressure on fishing stocks in European waters. Quotas were therefore introduced putting pressure on national fishing fleets. Each country was entitled to take steps to ensure that the owners of fishing vessels had a ‘genuine economic link’ with the industry. Amidst concern that the Spanish were buying up licences issued to British vessels, the UK parliament passed a law requiring a minimum level of British ownership to relate to vessels covered by such UK licences.
What is now our Supreme Court issued an injunction to suspend the law.

Lord Bridge said,

[European law and the law of the UK]
Some public comments on the decision of the European Court of Justice, affirming the jurisdiction of the courts of member states to override national legislation if necessary to enable interim relief to be granted in protection of rights under Community law, have suggested that this was a novel and dangerous invasion by a Community institution of the sovereignty of the United Kingdom Parliament. But such comments are based on a misconception. If the supremacy within the European Community of Community law over the national law of member states was not always inherent in the E.E.C. Treaty it was certainly well established in the jurisprudence of the European Court of Justice long before the United Kingdom joined the Community.
Thus, whatever limitation of its sovereignty Parliament accepted when it enacted the European Communities Act 1972 was entirely voluntary. Under the terms of the Act of 1972 it has always been clear that it was the duty of a United Kingdom court, when delivering final judgment, to override any rule of national law found to be in conflict with any directly enforceable rule of Community law.
Similarly, when decisions of the European Court of Justice have exposed areas of United Kingdom statute law which failed to implement Council directives, Parliament has always loyally accepted the obligation to make appropriate and prompt amendments.
Thus there is nothing in any way novel in according supremacy to rules of Community law in those areas to which they apply and to insist that, in the protection of rights under Community law, national courts must not be inhibited by rules of national law from granting interim relief in appropriate cases is no more than a logical recognition of that supremacy.’

[The Factual Background]
‘It is now, I think, common ground that the quota system operated under the common fisheries policy, in order to be effective and to ensure that the quota of a member state enures to the benefit of its local fishing industry, entitles the member state to derogate from rights otherwise exerciseable under Community law to the extent necessary to ensure that only fishing vessels having a genuine economic link with that industry may fish against its quota. The narrow ground on which the Secretary of State resists the applicants’ claim is that the requirements of section 14 of the Merchant Shipping Act 1988 that at least 75 per cent. of the beneficial ownership of a British fishing vessel must be vested in persons resident and domiciled in the United Kingdom is necessary to ensure that the vessel has a genuine economic link with the British fishing industry.
Before the decision of the European Court of Justice in Agegate that would have seemed to me a contention of some cogency. But in Agegate it was held that a licensing condition requiring 75 per cent. of the crew of a vessel fishing against the quota of a member state to be resident within the member state could not be justified on the ground that it was “irrelevant to the aim of the quota system:” I confess that I find some difficulty in understanding the reasoning in the judgment which leads to this conclusion. But if a residence requirement relating to crew members cannot be justified as necessary to the maintenance of a genuine economic link with the local industry, it is difficult to see how residence or domicile requirements relating to beneficial owners could possibly fare any better.’

Headings added for ease of reading. There is a full copy of all of the judgments and arguments including material relating to the European Court (now the Court of Justice of the EU) in the official law reports.