Special Branch - the counter-espionage arm of the colonial police - was infiltrated by Kuomintang spies plotting terrorist attacks on the mainland and in Hong Kong, intelligence reports released by the British government reveal.
The reports also show that Beijing tipped off Britain about Kuomintang operatives working in the city - at a time when the nationalist party still had aspirations of reconquering the mainland from its base in Taiwan.
The series of intelligence reports from 1962-63 - sent by governor Robert Black to the Colonial Office in London - were among files released last week on the administration of Britain's former colonies.
A report from January 1963 described the 'arrest of an inspector and a constable on the staff of Special Branch who, in league together, were supplying ... information on current Special Branch activities'. Both policemen - who were not named - 'admitted working on behalf of the KIS [Kuomintang Intelligence Service] for some years'.
Another two Special Branch detectives went 'under interrogation' after aiding KIS agents in June 1962.
Eight KIS agents were arrested in July 1962 before they could carry out 'two sabotage attacks, one on the railway between Canton [Guangzhou] and Hankow [Hankou ] and the other on the Canton/Shanghai express train, which were planned to take place on the same day'.
In September 1962, 32 people were arrested in connection with two KIS cells which were ordered to 'carry out acts of sabotage in China in support of a psychological warfare campaign'. Taipei believed Guangdong people 'were in the mood for insurrection and the time was ripe to seek to exploit disaffection within the southern provinces'.
China's Ministry of Foreign Affairs also gave a list of alleged KIS agents to Hong Kong 'against whom they asked that action should be taken', according to the May 1963 report.
Five of those listed were arrested, including one in possession of explosives, but two were released for lack of evidence. China handed over the list after a small explosion in the Astor Theatre in Hong Kong, where a mainland opera troupe had performed.
Black wrote in the telegram that Beijing's 'patience [with Hong Kong] ... is unlikely to be inexhaustible in [the] face of Kuomintang pinpricks'. He warned that 'something of a campaign against Hong Kong seems to be working up on other subjects - the situation is therefore potentially dangerous and very disturbing.'
KIS agents were often deported to Taiwan rather than prosecuted in Hong Kong.
Special Branch was disbanded in 1995 amid concerns over how it would be used after the handover.