Top judges charged with a landmark modernisation of the British legal system will be diverted from their task by an unlikely and perverse duty: serving on a court that is one of the country’s fustiest jurisprudential ­relics.

Lord Phillips, president of the new Supreme Court, said he was searching for ways to curb the “disproportionate” time he and his fellow senior justices spent hearing legal appeals from independent Commonwealth countries to the Privy Council in London.

The concerns highlight how the Supreme Court’s creation is a quintessentially British constitutional fudge, separating the judiciary from parliament for the first time but leaving intact a sister chamber widely seen as a post-imperial anachronism.

Lord Phillips said in an interview that he was concerned that the judges who will staff the Supreme Court from next month would – as during their previous incarnations as House of Lords justices – end up spending as much as 40 per cent of their working hours on Privy Council business.

He said: “It is a huge amount of time. I personally would like to see it reduced. It’s disproportionate.”

The president questioned whether some Privy Council cases, which have ranged from Jamaican death row appeals to fights over press freedom in Bermuda, needed to be heard by a panel of five of Britain’s most senior judges.

He said he was looking to take some of the pressure off the Supreme Court by drafting in Court of Appeal judges to help out, although he added that “in an ideal world” former Commonwealth countries would stop using the privy Council and set up their own final courts of appeal instead.

A creature of Britain’s 19th century colonial pomp, the Privy Council judicial committee is now used as a London-subsidised top court by about 15 independent nations, most of them small islands in the Caribbean and Pacific.

Many independent observers say this is both an ideological stain and a financial drain on the newly-created Supreme Court.

The Council judicial committee shares both the court’s handsome Parliament Square headquarters and access to the dozen judges whose £200,000-a-year day job is supposed to be resolving Britain’s most important criminal and commercial cases.

Robert Hazell, director of The Constitution Unit at University College London, said it was a “minor public scandal” that judges in the country’s top court spent almost half their time on business “of no interest to anyone in the UK”.

He said: “If they didn’t spend time in the Privy Council, the justices of the Supreme Court could hear almost twice as many cases coming up from the UK legal system.”

The Ministry of Justice declined to respond Lord Phillips’ comments, saying that how he ran the Supreme Court was a matter for him.