The court stated that the UK government had failed to prohibit the use of “marked fuel”, known in the UK as red diesel, “in private pleasure boats within the time limit prescribed by the European Commission”.

Such a ban had been introduced in 2018. Though the measure did not interfere with the ownership of houseboats, commercial ships, cruise liners or ferries, it would have affected owners of up to 150,000 private pleasure craft.

In 2020, infringement proceedings were brought against the UK, with a deadline to comply but the UK argued the proceedings were brought “prematurely”.

The CJEU said that the rule applied to the whole of the UK for some three years and that it was not relevant that it applied in Northern Ireland only since Brexit came into force in January 2021.

The court rejected arguments that the rule could not have applied between 2018 and 2020 due the general election in 2019 as well as problems during the pandemic.

“In that regard, the court recalls that the practical difficulties referred to by the United Kingdom cannot be taken into account as a mitigating circumstance,” the court said.

A UK government spokesperson said: “This is ultimately a historic case which began at a time when the UK was a member of the EU. We have now left. Since then, we have negotiated the world’s largest zero tariffs and zero quotas deal with the EU, and are now focused on using our Brexit freedoms to the benefit of the British public.”