British Foreign Secretary David Lammy has said he was deeply concerned after a UK lawmaker was denied entry to Hong Kong and said he would be urgently raising the issue with the Chinese authorities.

Hobhouse is a member of the Inter-Parliamentary Alliance on China.

"IPAC unites lawmakers worldwide, promoting democracy and addressing threats to the rules-based and human rights systems posed by the rise of China," the group says on its website.

The Sunday Times newspaper said Hobhouse, 65, flew to Hong Kong on Thursday on a personal trip to visit her newborn grandson.

It said she had her passport confiscated, was asked about her job and the purpose of her visit, had her luggage searched and was then taken to the boarding gate.

"Authorities gave me no explanation for this cruel and upsetting blow. I hope the foreign secretary will recognise that this is an insult to all parliamentarians and seek answers."

Hobhouse has been a member of parliament for the smaller opposition Liberal Democrats since 2017.

"It is deeply concerning to hear that an MP on a personal trip has been refused entry to Hong Kong," Lammy said.

"We will urgently raise this with the authorities in Hong Kong and Beijing to demand an explanation." As I made clear earlier this week, it would be unacceptable for an MP to be denied entry for simply expressing their views as a parliamentarian.

It comes as Hong Kong's Democratic Party, once the city's stalwart opposition force but now seatless, is preparing to dissolve as some of its veterans languish in jail.