Eleanor Sharpston QC told The Guardian that a vote to leave the EU would deprive the European Court of Justice (ECJ) of some of its best talent.

She also denied European judges deliver the final verdict in cases and cautioned over the powers of national constitutional courts.

The ECJ was founded in 1952 as the Court of Justice of the European Coal And Steel Communities.

Ms Sharpston, a fellow of King’s College, Cambridge and formerly joint head of a London chambers has been a member of the court since 2006, making her the longest serving UK judge at the court ever.

She said: “The UK has made a very strong contribution to this court and the evolution of EU law since it joined in terms of injecting a degree of pragmatism.

“The procedures of this court and the way it deals with cases have been improved by the addition of the common law tradition into the mix.

“Some very good people have served in the court – Lord Gordon Slynn, Sir Konrad Schiemann and Sir Francis Jacobs – and they have made a difference.

“It would be a pity to lose this contribution … The quality of what is done within EU law is enriched by having a strong contribution by good common law coming from the UK and Ireland.”

She agreed the court has become more prominent, with a caseload exceeding 700 for the first time last year.

“Various things are happening simultaneously.

“Over the years other competences have come within the field of EU law … by common agreement of EU states. It’s not that the EU grabbed new powers…

“ we get cases which are about immigration, asylum and European arrest warrants … All of this is much closer to the core business of Strasbourg. EU law is engaged in a wider range of topics now because that’s what member states wanted. There are more cases where there may be fundamental rights aspects,” she added.

But Ms Sharpston disagreed with the view that constitutional courts interfere in the relationship between national courts and the EU, saying: “We are perfectly aware that the judges of the German constitutional court have their judicial oath,.

“It doesn’t cause us trouble. They are not trigger happy with it. It’s not a general enabling power to disapply they don’t like. It’s a very specific protection and they operate it as that.”

As an advocate general, Ms Sharpston, who is paid €240,000 (£191,000) a year, provides initial opinions. In the majority of cases these are followed by the court.