Hong Kong's sole delegate to the National People's Congress Standing Committee (NPCSC) said on Saturday China's top legislative body would need to interpret the law if admission of overseas lawyers was allowed in national security cases.

Tam Yiu-chung's comments come as the city's top court is due to announce on Monday whether it will grant leave for an appeal from the government that seeks to ban King's Counsel Tim Owen from defending former media tycoon Jimmy Lai at his trial.

Asked about the matter, Tam said it would be inappropriate for overseas counsel to be admitted in the case, saying that would go against the original purpose of the security legislation – which was to prevent people from endangering national security, sovereignty, and development interests.

He said the top legislative body would be obliged to explain the original purpose of the legislation if it were misunderstood.

"National secrets and issues of foreign forces may be involved during the case's trial," Tam told reporters. "So I think foreign lawyers should not be allowed to take part in it."

"If the situation remains unchanged, there is no other way but for the NPCSC to interpret the law and make adjustments regarding the issue."

The local Court of Appeal previously rejected two government bids to block Owen from representing Lai.

Tam denied that he was pressuring the Court of Final Appeal, saying he was just expressing his views as someone who took part in the legislation work for the security law.

"I understand the original purpose of the legislation very well... We thought the law very important and so we drafted it in Chinese. The English [version] is only for reference. For some foreigner who doesn't know Chinese to be admitted in a case concerning Chinese national security, we think it would not be appropriate."

Lai, the founder of the now-defunct Apple Daily newspaper, will face trial for allegedly taking part in a conspiracy to print and sell seditious publications, as well as conspiring with others to collude with a foreign country or external elements to endanger national security.

The 30-day trial is scheduled to begin on December 1.