Hong Kong police have charged seven officers with assaulting an activist whose beating, caught on camera, stirred outrage among city residents at the height of pro-democracy protests last year.

The seven officers were charged jointly with one count of grievous bodily harm, and one was also charged with common assault. They are due to appear in a magistrates court on Monday.

The activist, Ken Tsang, was among a group of people involved in a clash with police during protests over Beijing’s plans to restrict elections.

Tsang was charged on Thursday with one count of assaulting an officer and four counts of resisting police. The charges relate to moments before the beating, when officers attempted to apprehend Tsang as he splashed liquid from a bottle on police, the justice department said.

The accused officers, all men aged between 31and 48, were working in plainclothes at the time. The charges are being brought exactly a year after the incident.

In the early hours of 15 October 2014 as protesters and police battled for control of an underpass outside the government headquarters, the local station TVB recorded officers taking a handcuffed Tsang behind a building in a nearby park.

The video shows the officers placing Tsang on the ground, then one punches him while several others kick him.

The officers were suspended from duty in November but Tsang’s supporters accused authorities of dragging their feet after the investigation stalled.

“This is a kind of political pressure,” Tsang told reporters before entering the police station on Thursday. “Very simply the purpose is to make the plaintiff become the defendant” and distract the public, he said.