Jimmy Lai, Hong Kong's pro-democracy media tycoon, has won an appeal against a fraud conviction in 2022, which had seen him sentenced to nearly six years in jail.

On Thursday, Hong Kong's Court of Appeal quashed the convictions of Lai and another defendant who had been accused of illegally subletting office space.

But the 78-year-old will remain in prison. Earlier this month, he was sentenced to 20 years in jail for colluding with foreign forces under the city's national security law.

Lai, a British citizen, is a fierce critic of Beijing and is one of the biggest figures in Hong Kong's pro-democracy movement. He has been detained since 2020.

Lai's daughter Claire described the ruling on Thursday as "nothing more than a PR move by the Hong Kong authorities".

"No one should be fooled into thinking.. [it] is anything more," she told the BBC.

"The rule of law is broken there, and my father is still unjustly imprisoned and will remain so for nearly 20 years unless urgent action is taken to secure his release."

Caoilfhionn Gallagher KC, who leads Lai's international legal team, echoed this, saying the decision "changes nothing" and that Lai risks dying in prison because of ill health.

"No one should be fooled into thinking that this fraud appeal belatedly succeeding suggests the Hong Kong system operates fairly or justly," she told the BBC.

In 1995, Lai founded Apple Daily, a local tabloid that was critical of Beijing and became Hong Kong's largest pro-democracy paper. The paper was shuttered in 2021 after Lai and other key staff members were arrested.

The paper was at the heart of Lai's fraud trial. Prosecutors argued that Lai breached lease terms by allowing his private consultancy firm to operate in office space that Apple Daily had rented.

Wong Wai-keung, a former executive at Lai's media company, was also charged in the same case and jailed for 21 months.

Critics say Lai's trials and detention are a sign of the shrinking civil liberties in Hong Kong, especially after the introduction of a Beijing-imposed national security law.

This month, the UK and the US governments said the national security law has been used to "silence" activists like Lai.

But Beijing and Hong Kong authorities have argued that the law is necessary to maintain stability and deny it has weakened the territory's freedoms as a semi-autonomous region of China.

Rights groups and Lai's family have raised concerns about his deteriorating health in prison. Last December Claire Lai told the BBC that her father's teeth were rotting and his fingernails "sometimes fall off".

But Chinese authorities maintained that Lai was "in good health" and received "appropriate" care.

Supporters claim that Jimmy Lai has long been facing political persecution through the courts. The overturning of the sentence on Thursday has been met with some scepticism by some.

"Even if [he] is released at 96 rather than 98, it doesn't make much difference," one supporter who attended court told the BBC.