Nathan Law began 2020 planning a new run for office in Hong Kong. He has ended it a political exile in Britain, unsure if he will ever be able to return to the city he calls home, or speak to his family again, because of his work campaigning for democracy.

The end of the year has been particularly painful for the 27-year-old. He has watched from the other side of the world as friends in Hong Kong, including Joshua Wong and Agnes Chow, have been jailed for their campaign work. He has been unable to send them even an email of support.

The sweeping new national security law passed by China this summer, which prompted Law’s flight and has been used to crack down on the city’s protest movement, criminalises, among other things, “collusion with foreign powers”. Because he lobbies governments around the world to support Hong Kong’s pro-democracy movement, he fears if he does contact them, another offence could be added to the list of charges against them.

“I can’t communicate because it may endanger them,” he said in a phone interview. “It makes it harder to know you can’t offer help or give spiritual help directly; that’s a source of guilt; it makes the days very grim.”

The only way he knows to deal with it is by doubling down on the campaign work that put them in jail and forced him into exile. “If I can’t help them in that way I have to do it in another way, which is doing more in advocacy work.”

Despite his youth, Law has for years been one of Hong Kong’s most high-profile pro-democracy campaigners, part of a small group that serve as figureheads for a movement that officially has no leaders. As a co-founder of the now-disbanded Demosisto party, which fought for self-determination for Hong Kong, he has spent time in the city’s jails and on its legislature.

In 2016, he won office as the youngest lawmaker in Hong Kong’s history, but was disqualified almost immediately by pro-Beijing authorities, who said he had behaved improperly while taking his oath of office. The following year, he was jailed for several months, along with Wong and others, over his role in the “umbrella movement” protests of 2014, which ended with few tangible political gains but shaped a generation of student activists. In 2019, he began a master’s at Yale, which he finished earlier this year mid-pandemic and mid-protests. He returned in March to a city in turmoil, the pro-democracy demonstrations paused by Covid controls, but its spirit undiminished.

After a city-wide landslide for pro-democracy candidates in district elections last autumn, he wanted to attempt another run for the legislature again. Barely three months later though, he would be on a plane to Britain, after an ominous trickle of news about the new security law convinced him that the movement needed a representative who would be beyond the reach of Chinese authorities.

It would not be the first time that a move across borders would radically change the direction of his life. Law was born in the southern Chinese city of Shenzhen and only moved aged six to Hong Kong, the city that would come to define his identity and give him a self-declared political “vocation”.

But this time the decision was his alone and it would be irrevocable. “It could be an eternal goodbye; no one knows when I can go back,” he says bluntly. The separation has been particularly painful because he also cut all ties with his family, over fears Chinese authorities might pressure them for his work.

He had only a couple of weeks to make up his mind, convinced that under the new law he would be likely to face charges. “I had to contemplate, mostly by myself, to really see if I’m ready. I had to think of friends, family, what I established in the political arena, all my attachment to the place. It was really not an easy decision to make. I had to think about our organisation’s future. We still need a voice on international level that is recognised, so we have that kind of representation.”

Those fears were confirmed in August, when he was named on an international “wanted” list for crimes including “collusion with foreign powers”, a reference to his international lobbying. The security law has since been deployed to crush dissent and stifle freedom of speech, targeting pro-democracy journalists and politicians, academics, protesters, even teachers and other professionals.

A crackdown had been expected, but not the scale of China’s intervention. “It was a shock for every one of us,” Law says. “I don’t think any political commentator in Hong Kong saw that coming. The degree of its impact has also far exceeded our judgment in terms of how Beijing would act.”

Law knows there is little hope that recent changes in Hong Kong will be reversed soon. But he sees his struggle as part of a broader fight for democracy across all of China and finds cause for hope in the international outcry at his city’s fate, which his relentless campaigning aims to keep on the front pages.

In Britain, he points out, it was only a few years ago that David Cameron declared a “golden age” in relations with China and president Xi Jinping was welcomed at Buckingham Palace.

“It has never been a short-term fight for me; it may take decades to return to a democratic and free Hong Kong,” he says. “We have to make sure when people think of China they don’t think of economic growth, business opportunities - they think of concentration camps in Xinjiang, the struggle of Hong Kong, people inside mainland China jails.”

Personally, he is slowly adapting to the shift from sub-tropical Hong Kong to the overcast days of a London winter. The city has been welcoming, even in lockdown, helped perhaps by the shared physical infrastructure of his home.

“There is the language and the colonial legacy – the vehicles, the road signs, the traffic lights, the sockets – these small things remind you of Hong Kong,” he says.

He may be spending less time here, though, once vaccines allow life to return to something like pre-pandemic normal; since arriving in London, lobbying has already taken him across Europe and he has testified to American lawmakers by video link.

With friends and allies in Hong Kong jailed or facing charges, he is even more determined to use his freedom to build on the international support they have gained this year and urge more policy steps such as US sanctions against top officials and Britain’s offer of a path to citizenship for millions of Hong Kong residents.

“For me, the most important thing is to be patient, to keep going and not lose hope. And these little encouragements could be the [impetus] for me.”