The decision comes as powerful establishment voices call for an overhaul of the judiciary – something opponents fear could muzzle the Hong Kong legal system’s vaunted independence as Beijing cracks down on critics.

Friday’s ruling by the Final Court of Appeal is the culmination of a long legal battle by Leung Kwok-hung, 64, who served a brief jail sentence in 2014 linked to his protesting.

Better known by the sobriquet “Longhair”, he is one of the city’s best-known dissidents, beginning his career campaigning against British colonial rule and later becoming a fierce critic of Beijing.

A panel of top judges – including Chief Justice Geoffrey Ma – unanimously ruled that Leung’s rights had been breached under sexual discrimination laws when his hair was cut in jail.

Hong Kong prison authorities insist all male inmates keep their hair cut short, but female convicts are allowed to grow theirs long if they wish.

“The fact that male prisoners are denied a choice as to their hair length, suggests that they are treated less favourably than female prisoners,” the judges wrote, adding authorities had failed to explain why short hair was required for custodial discipline.

The decision comes at a sensitive time for Hong Kong’s legal system.

Unlike authoritarian China’s party-controlled judiciary, the city maintains an independent common law system that forms the bedrock of its success as a global trade and finance hub.

But two leading pro-Beijing newspapers in the city – and a vocal group of pro-government politicians – have recently begun calling for reforms to the judiciary.

Earlier this month those calls won backing in a speech by Zhang Xiaoming, a senior Chinese official responsible for the central government’s policies towards Hong Kong.

Beijing loyalists have been incensed by recent acquittals of some protesters – often by judges with harsh words to say about police behaviour and evidence gathering – and judicial reviews that have gone against the government.

Last week a High Court judge delivered a damning ruling against police in a case linked to last year’s huge and often violent pro-democracy protests.

The judgement, which can still be appealed, found that officers were wrong to hide their identification badges and that the city’s watchdog has been “inadequate” in investigating complaints against officers.

Staunch pro-Beijing newspaper Ta Kung Pao ran a scathing report on the ruling under the headline “Thugs rule, no human rights for policemen”.

That article sparked a call from the influential Bar Association for the government to vocally defend the judiciary’s independence.