The news yesterday from protests in Hong Kong is extremely worrying and demands a response from UK parliamentarians. This concerns not just the welfare of an 18-year-old, shot in the chest at close range by the police, but also the future of democracy in a country whose history is closely linked with the UK's.

The immediate events leading up to the shooting, and whether the police officer acted in self-defence, will need to be examined in detail. Nonetheless my thoughts, as a parent of two sons, are with the family holding vigil at the Queen Elizabeth Hospital in Yau Ma Tei.

There has been a tragic escalation of tensions, and Hong Kong has become a tinder box. The explosion of anger today should be condemned, but it is the result of the brutal actions of the authorities to what were initially peaceful protests. It is particularly worrying to see credible reports that China has doubled the number of troops in Hong Kong to 12,000.

The root causes are of course nuanced and complex, and the UK must share some responsibility. Many protesters have been locked up arbitrarily by the authorities, for up to 10 years in some instances, under a public order ordinance that is a hangover from our 150-year colonial rule.

In the UK we must continue to defend the interests of ordinary citizens, over 100,000 of whom have British National (Overseas) passports, but no right to live in the UK.

In 1984, a series of assurances were made to the UK Government which paved the way for the handover in 1997. These were codified in the Sino-British Joint Declaration, an international treaty lodged with the United Nations. This protected the human rights of the people of Hong Kong, including the rights to free assembly and freedom of speech. The 'One Country, Two Systems' arrangement was intended to reduce the fears of Hong Kongers worried about Chinese government pressure on their democratic rights, but it has effectively collapsed.

It is important to understand how frightening it must be to live in Hong Kong today. If you were one of the two million people (in a region of seven million) who have been on the streets over the last 100 days to demand basic human rights and universal suffrage, there is a good chance that you would have seen your friends and family beaten, sprayed with tear gas and arbitrarily arrested.

Those taking part in legitimate protests have had to wear masks for fear of being kidnapped and taken to mainland China for a pre-arranged show trial. Last week in London an estimated 1,500 people marched peacefully in solidarity from the Chinese Embassy to Trafalgar Square, calling for fundamental human rights to be protected.

The overwhelming majority of protesters are students and young professionals who have crowdfunded support via NGOs such as Stand With Hong Kong and Hong Kong Watch, of which I am a patron. Their only crime is to want to change their world – to enjoy the same freedoms we do in the UK.

One of the demands of the protesters is for the UK Government to make a clear and unambiguous statement that the Sino-British Joint Declaration has been breached, and that China is therefore in breach of international law. This is a point that my party, the Liberal Democrats, has been making for some time. With China’s denial of basic freedoms and rights in Hong Kong, the case appears to have been met, prima facie.

Our friends in Hong Kong are facing a fight for their freedom and their lives. We must stand with them in that fight and in their campaign for genuine democracy through universal suffrage.