The daughter of Jimmy Lai, the pro-democracy tycoon jailed in Hong Kong, has expressed concerns about her father's deteriorating health in prison, saying that his fingernails sometimes fall off and his teeth are rotting.

Lai, 78, has been detained since December 2020 and faces life in prison. Earlier this month he was convicted of colluding with foreign forces under the city's controversial national security law (NSL).

Chinese authorities have denied that Lai has been mistreated in prison, and said he is in good health.

The BBC has seen a letter written by Lai's family urging UK Prime Minister Keir Starmer to call for Lai's release when he meets Chinese President Xi Jinping next month.

His daughter Claire Lai, who's in exile in London, told the BBC that she fears she may never see him again. Of course I worry that my father is going to be a martyr, and I don't want him to be a martyr. But I would not be here today, I would not be speaking out if I didn't think this was his best chance of reuniting with our family, she stated.

Claire described her father as an extremely robust and strong man when he went to prison, but over the last year, he has lost a significant amount of weight. He is diabetic, he has heart issues which he never had in the past. He has fingernails that turn purplish grey and sometimes fall off. He has teeth that are rotting. He has back and waist pains. Some days it's painful for him to stand. Sometimes he can't stand. And some days he can't even get out of bed, she added.

Lai's family has repeatedly voiced concerns about his declining health, with his son Sebastien also commenting that his father's body is breaking down.

A spokesperson for the Commissioner's Office of the Chinese Foreign Ministry in Hong Kong stated earlier this month that Lai's lawful rights and interests have been fully protected, and he is in good health and that he is provided a safe, humane, appropriate, and healthy custodial environment in accordance with the law.

Lai, a UK citizen, is the most prominent person to be charged under the NSL, which was introduced in 2020 following massive pro-democracy protests in Hong Kong. Beijing defends the law as necessary to maintain stability, while critics argue it essentially criminalizes dissent.

After Lai's recent conviction, the UK condemned the ruling as politically motivated persecution, asserting that he has been targeted for peacefully exercising his right to freedom of expression. The UK government has continuously called for the NSL to be repealed and for an end to the prosecution of individuals charged under it.

Starmer's trip to China in late January 2026 will mark the first visit by a UK Prime Minister since 2018, throwing additional pressure on the topic of human rights in the region.