They had originally been charged with grievous bodily harm with intent.

The activist, Ken Tsang, was part of a group of protesters involved in a pre-dawn clash with police outside government headquarters over Beijing's plans to restrict elections for the semiautonomous city.

During the scuffle on October 15, 2014, television news cameras caught officers kicking and punching a handcuffed Mr Tsang in a dark corner of a nearby park.

Mr Tsang himself was convicted last year of assaulting police and resisting arrest in relation to the incident and sentenced to five weeks in prison.