A police officer accused of hitting a student over the head with a baton during a protest nine years ago has been cleared of misconduct, after a panel found an unidentified colleague struck the blow.

Alfie Meadows, 29, who was then studying philosophy at Middlesex University, needed emergency surgery after sustaining a serious brain injury.

Detective Constable Mark Alston, 37, was cleared of wielding his "baton in a violent, uncontrolled and dangerous manner" and using unreasonable force to hit Mr Meadows over the head.

Video footage captured the City of London Police officer striking his weapon four times towards protesters during the demonstration against student fees in London on December 9 2010.

But a three-person panel cleared him of misconduct on Thursday following a hearing in central London, finding that a Metropolitan Police officer, who has never been identified, caused the injury.

The chairman, temporary Deputy Chief Constable Nev Kemp, said Dc Alston's actions were an "instinctive reaction to the surge of the crowd, which he was tasked with holding back, in order to protect himself and his colleagues".

"We are clear Mr Meadows suffered a serious head injury and that his injury occurred during the demonstration," he said.

"Furthermore, on the balance of probabilities, we find Mr Meadows was struck by a police baton rather than another object."

The panel said footage of the incident appeared to show Dc Alston's baton striking to the right of where Mr Meadows was standing.

"The baton of the Met Police officer appears to strike in the area where we believe Mr Meadows's head was," Mr Kemp said.

"We find therefore Mr Meadows was struck by a police baton to the head but the strike was performed by a Met Police officer and not Pc Alston.

"It is not for us to consider whether his actions were justified and we say nothing more about it."

Speaking after the hearing, Mr Meadows, who is studying for a master's degree in philosophy, called on Scotland Yard to now identify the Met officer seen in the video.

"I have had to fight for almost a decade for accountability after almost being killed by a police officer," he said.

"This panel found that a police officer's baton caused my injury and that what I have been saying the whole time is true.

"However, I think it's unaccountable they decided to apportion partial responsibility to the unidentified Met Police officer."

Dc Alston was a 26-year-old Pc when he was deployed to police the protest, which saw violent clashes in and around Parliament Square.

Mr Meadows was one of more than 10,000 people demonstrating on the day of a parliamentary vote to raise student fees when he was struck in the head.

He needed more than 100 staples in his head and was left with a large scar, but was charged with causing violent disorder and taken to court where he was cleared by a jury in 2013.

A probe by the police watchdog, now called the Independent Office for Police Conduct (IOPC), found Dc Alston had a case to answer for gross misconduct.

But City of London Police rejected the recommendation, then failed in a court bid to challenge the IOPC's direction that he should face a full hearing.

Giving evidence, Dc Alston said he went into the crowd with colleagues to rescue a group of officers, while missiles were "raining" down, and feared he could be injured by metal barriers being pushed towards him by protesters.

"I was in a situation where I believed my life was at risk and that of other officers. I was in a situation which was really crowded," he said.

"I was trying to do my best to defend myself and my colleagues."

Mike Reed, chairman of the City Of London Police Federation, said the outcome of the hearing came as "no surprise" but was a relief to Dc Alston and his family.

"Dc Alston was being judged on an incident that occurred just over nine years ago ... which lasted seconds," he said.

"Police officers have no issue with being held accountable for their actions, we are the most accountable of public services. But how can it be just or justified to have your life put on hold for so long?"

A spokesman for the IOPC said: "Today the panel agreed that there were two officers wielding their batons in close proximity to Mr Meadows at the time he received his injuries. However, it ruled that Pc Mark Alston was not responsible for delivering the strike that caused Mr Meadows' serious injuries. The panel determined that a Metropolitan Police officer who has never been identified, despite strenuous and exhaustive enquiries on our part, was responsible.

"Despite a legal challenge against our decision that Pc Mark Alston had a case to answer for causing Mr Meadow's injury, the courts agreed with us that he should face a police disciplinary panel. We found that he had a case to answer just over a year after he was identified as one of the officers in the footage.

"The public has the right to expect police officers to be accountable when they use force, particularly if it leads to a death or serious injury and we directed that this hearing should be held in public.

"This has undoubtedly been a difficult journey for all involved."