Now, in my opinion yes.
By the way, if you want an unbiased article then you should visit Adam's column. Although, he is slightly left wing. He is somewhat less biased than me, in his writing that is.
The U.K. left her former colony in the year 1997, after long and time consuming negotiations surrounding the rights of the people of Hong Kong. The U.K., in fear, gave all of the people living in Hong Kong a U.K. passport and citizenship as a result of fears for their rights and liberties.
However, China has kept to it's word and kept it's large and growing nose out of the rights and liberties of the people of Hong Kong, for now.
This is a result of the U.K. and China signing an agreement (the Sino-British joint declaration), which meant that china would not interfere in the deeply capitalist policies of Hong Kong for 50 years until 2047. Which, The People's Republic (China) have kept to, even in the face of mass protests as seen in Hong Kong this year.
So, does the UK have a legal responsibility?
YES it does- it is a signatory of the joint Sino-British declaration and as a signatory it must uphold the agreement. Even if this means ruining Sino-British trade deals as a matter of principle!
However, you might argue that Hong Kong is no longer a responsibility of the UK as it's under foreign rule. But, Libya was under foreign rule. We still bombed them and overthrew longstanding president- Colonel Gaddafi. What is different with the case of Hong Kong? Except, obviously, no one is being murdered and there is no civil war but the same basic ideals apply, such as:
So, overall it seems that, yes, the U.K. should stand up for the rights of Hong Kong citizens, both because, we the British have signed a treaty and therefore we are legal signatories but also out of principle. As the U.K. with the mother of all parliaments surely has a certain amount of duty to give the people of the world the right to self determination.