A new paper by the Adam Smith Institute says Hong Kong nationals should be given British citizenship rights.

The United Kingdom has a duty under the Sino-British Joint Declaration to uphold the rights of Hong Kong citizens until 2047 as a joint signatory and ex-colonial power.

While the United Kingdom cannot act within the territory of Hong Kong it can still act to maintain and enhance the rights of Hong Kongers within the territory of the United Kingdom.
The United Kingdom should offer British National (Overseas) status to all Hong Kongers born before and after the 1997 handover, along with an extension of full residency rights to British National (Overseas) persons equivalent to the status of full British citizens.
This would follow precedent in the face of extreme violence to ex-British citizens as seen in Uganda in the 1960s and 1970s.
Hong Kong residents, with high levels of education, skills and wages would be a net contributor to the UK economy.
The Chinese Government would face an increased incentive to act leniantly to Hong Kong in order to not lose face should a large number of citizens choose to abandon rule from Beijing.