The police force whose officer struck a young black woman 'as hard as I was physically able' as he arrested her said it was outraged at the suggestion that it was a racist incident.

Pc Anthony Mulhall, of South Yorkshire Police, said he used "brute force" as he hit 20-year-old Toni Comer to subdue her so she could be handcuffed.

Ms Comer is pursuing a civil action against the force after the incident outside the Niche nightclub in Sheffield last July was captured on CCTV.

A South Yorkshire Police spokesman said: "We are satisfied with the way this incident was handled and happy with the conduct of the officer, but we will investigate the circumstances of the complaint."

He added: "The force is outraged at the nature of the report itself and the possible suggestion that this may be linked to any kind of racist incident." The force will consider the incident further.

Chief Superintendent Ali Dizaei, of the National Black Police Association, called for an investigation by the Independent Police Complaints Commission, saying that it was "absolutely" a concern that race may have been an issue.

But he said that while the video looked "appalling" at first glance, it was acceptable for officers to use force of the kind seen if it was necessary to stop the person being arrested harming themselves or someone else.

Mr Dizaei said the incident ought to be investigated by the IPCC but added that officers have got to use "reasonable force" to prevent injuries.

Shami Chakrabarti, director of Liberty, said: "These images turn the stomach and raise serious questions about police misconduct. The IPCC must investigate urgently in the knowledge that public confidence in modern policing and the police complaints system is at stake."

The CCTV footage, obtained by The Guardian and shown on BBC2's Newsnight, shows Ms Comer and a police officer falling down a flight of stairs outside the nightclub in Sheffield, with the officer landing on top.