The loss of British justices from Hong Kong's top court will tarnish its international reputation as a common law jurisdiction and reduce judicial manpower, a leader of the city's legal community explained.

"If the British non-permanent judges were not to come, that would be quite a blow as they are the majority of overseas judges here," Philip Dykes, local barrister and chairman of the Hong Kong Bar Association, said in an interview with Business Times on Wednesday.

"It would cause huge reputational damage to Hong Kong that the Foreign Secretary believes British judges can no longer come here without participating in a compromised system," he added.

The possibility was floated by British Foreign Secretary Dominic Raab in a bi-annual report on Hong Kong published by the UK government on Monday.

"I have begun consultations with Lord Reed, president of the UK Supreme Court, concerning when to review whether it continues to be appropriate for British judges to sit as non-permanent judges on the Hong Kong Court of Final Appeal," Raab wrote in the report, urging mainland authorities to respect Hong Kong's autonomy.

The UK "must wake up from its colonial nostalgia," a spokesperson for Chinese Foreign Affairs Commissioner Xie Feng said in response.

The presence of judges from other common law jurisdictions has long been touted by Hong Kong chief executive Carrie Lam as proof of the city's judicial independence.

But this was cast into doubt when Australian Justice James Spigelman resigned in September owing to concerns about the recently passed National Security Law he said in an interview with ABC.

Likewise, "the National Security Law and recent events in Hong Kong have, in (Raab's) view, compromised the independence of the judiciary institutionally," Dykes explained.

The UK Foreign Secretary "is concerned with justices continuing to sit in a jurisdiction which has now been blighted by serious breaches of the Joint Declaration."

The most recent breach occurred in early November, when the National People's Congress in Beijing passed a resolution updating the oaths legislators take before assuming office to emphasize 'patriotism' - four elected members of the opposition were immediately disqualified and another 15 resigned in protest.

While the NPC's ruling focused on lawmakers, judges in the city also take an oath and any potential alterations bode poorly for overseas justices serving Hong Kong.

"The emphasis on patriotism is a bit disturbing because it affects the wording of the judicial oath," Dykes said. "My concern is that any revision requiring tests of loyalty could...prevent foreign nationals from taking their oaths."

But as foreign judges are invited on an individual basis to sit as non-permanent members of the court, the decision is theirs to make.

"Ultimately it's for the judge to decide to sit here, take the judicial oath which judges here are required to take and do it with a clear conscience."