A former employee of the British Consulate in Hong Kong says he was detained and tortured by Chinese secret police trying to extract information about massive anti-government protests in the territory.

Simon Cheng said in an online statement and media interviews that he was hooded, beaten, deprived of sleep and chained to an X-shaped frame by plainclothes and uniformed agents as they sought information on activists involved in the protests and the role they believed Britain played in the demonstrations.

British Foreign Secretary Dominic Raab has summoned the Chinese ambassador in London to express the government's outrage and demand Beijing investigate and hold those responsible accountable.

Chinese police in August announced Cheng's release after 15 days of administrative detention but gave no details of the reasons behind his detention.