The government is set to submit local legislation for a joint checkpoint at the West Kowloon terminus of the Guangzhou-Shenzhen-Hong Kong Express Rail Link to the Legislative Council by next month, as it is gunning for the rail link to start operations in the third quarter of this year.

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But the city’s legal experts maintain that the plan, known as co-location, contravenes the Basic Law.

The city’s mini-constitution, they have highlighted, states that barring a few exceptions, mainland laws must not be applied in Hong Kong. The exceptions include laws that relate to defence, foreign affairs and “other matters outside the limits” of the autonomy given to the city.

Cheng’s comment on what the courts could do was in contrast to the most recent statement on the matter by a mainland official.

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Cheng, who was interviewed on Commercial Radio, did not say whether the NPCSC’s approval of the Hong Kong government’s plan, given last month, could be challenged. But she noted that it had made its decision in accordance with China’s constitution – which Beijing had previously stressed that Hong Kong must respect as the ultimate legal authority.

Asked if there was legal basis for co-location, Cheng said: “There is, and there should be ways to do it without going against the Basic Law.”

She did not elaborate further, but said she hoped to better communicate with lawyers and Hongkongers to understand it.

Ronny Tong Ka-wah, a barrister and member of the Executive Council – which advises the city’s leader on policy – said Cheng and Zhang’s remarks were not contradictory.

“Teresa was saying that the courts have jurisdiction on Hong Kong’s legislation,” he said.

But, he continued in reference to Zhang’s comments, “they do not have jurisdiction over the constitutionality of the NPCSC’s decisions.”

Tong said it was possible that any legal challenge to co-location would end ultimately in Beijing making the controversial move of interpreting provisions of the Basic Law, which the NPCSC has the power to do and which the city’s courts would have to follow.

Legal experts had previously said that if it had to issue an interpretation on co-location arrangements, the NPCSC would say the plan was constitutional.

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The Bar Association – the city’s barristers’ guild – and the Law Society, a professional body of solicitors, had warned that the plan risked undermining the Basic Law and the “one country, two systems” principle of governance, under which Hong Kong gets a high degree of autonomy.

On Sunday, criminal law expert Lawrence Lok Ying-kam SC, newly elected to the board of the Bar Association’s council, said: “Let’s not focus too much on the very airy stuff that on the surface, may appear to be related but is actually not really relevant, for example, that the Hong Kong government is spurring employment, business opportunities, things like that.

“They need to persuade us: why at a train terminus in Kowloon West, can mainland Chinese laws be enforced?”

He said that the group would be willing to meet with Cheng to discuss co-location.

Cheng explained on Sunday that the ongoing row over co-location was why she had decided to skip last week’s meeting of the Legislative Council’s legal services panel – which scrutinises legal policies – and only attend next month’s meeting.

Cheng explained she needed time to first speak with the Law Society and Bar Association, which elected a new chairman last Thursday.

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She added that there was a “misunderstanding” between her and lawmakers on the matter.

But Civic Party leader Alvin Yeung Ngok-kiu said Cheng’s explanation was “unconvincing”.

“Cheng seems to have forgotten that she’s entered politics and she’s now a politician ... If there is no issue concerning her integrity, that could be the reason for postponing her meeting in the legislature. “But now her role has been causing a lot of concern,” Yeung said.

​Panel member Felix Chung Kwok-pan, leader of the pro-establishment Liberal Party, said: “It’s her decision, but it’s favourable for her to come to the Legco as soon as possible to answer questions.”

Additional reporting by Ernest Kao