A photograph emerged last week allegedly showing the newspaper vendor Ian Tomlinson with a head injury before his death during this April's G20 protests.

The latest blurred image shows the newspaper seller on the ground with what appears to be a large wound or bruise on the right side of his forehead.

Speaking to The Journal, the director of Liberty, Shami Chakrabarti said: “Clear images of an armoured policeman assaulting an innocent bystander from behind impugn the whole attitude to policing protests by the Metropolitan Police. The IPCC failed its first major test in the Menezes case. If the Commission is to regain a shred of public confidence it must do far better in terms of speed, sanction and transparency.”

Forming an additional piece in this highly complex puzzle, the evidence remains consistent with video footage that has already revealed how his head hit the ground after being pushed over by a police officer.

The footage showed he was walking away from police with his hands in his pockets when he was hit from behind by the Metropolitan police officer. The 47 year-old was helped to his feet by passers-by and walked off, seemingly not seriously hurt.

The photograph revealing the injury was taken three minutes later, as police medics tried to revive him after he collapsed nearby.

Sky News has now passed the photograph to the Independent Police Complaints Commission (IPCC). When asked whether it would form part of the investigation, an IPCC spokesman said: “We’re looking at lots of CCTV and images from various places, but we’re not going to give a running commentary on an ongoing criminal investigation.”

This new evidence comes to light just two days after a third post-mortem examination was carried out on the body of Mr Tomlinson.The results have yet to be disclosed.

It was only after conflicting results emerged from the first two examinations, that arrangements for a repeat investigation were made by the lawyer of the suspended police officer in question.

The first post-mortem examination was carried out by Dr Freddy Patel, who concluded that Mr Tomlinson died from a heart attack after he collapsed during the G20 protests on 1 April.

The second post-mortem carried out at the request of Mr Tomlinson’s family and the IPCC rejected such findings. Dr Nat Carey later found Mr Tomlinson to have died from internal bleeding. Such conclusions have prompted IPCC investigators to question the officer in connection with Mr Tomlinsons’s death on suspicion of manslaughter.

A Metropolitan police pathologist observed the post-mortem after a request from Scotland Yard, and the body will now be returned to Mr Tomlinson’s family.

The IPCC have now confirmed that 185 complaints against police behaviour during the protests have been made, of which 52 are being investigated.

The IPCC is conducting a further three specific investigations into incidents around the G20 protests: alongside the death of Mr Tomlinson are allegations made by Ms Fisher, and a complaint by a 23 year-old man who has not been named.

Thousands of hours of police video footage from the G20 protests are currently being studied for possible incidents of police brutality or misconduct. Whilst a review of public order tactics, especially the use of “kettling” where protesters are herded by officers into a confined space, will also be assessed.

Ms Chakrabart, of Liberty condemned such tactics: “We have serious concerns about “kettling” human beings in difficult situations. Surely if you have public order concerns it’s better to disperse a crowd than trap people in a confined space. Imprisoning them in this way risks making people angry, making them desperate and exacerbating any risk to public safety.”

Chairman of IPCC, Nick Hardwick contended that, as part of the Territorial Support Group, a specialised force trained in public order amongst other specialist policing, officers are in fact trained to hit protesters.

However, as a Metropolitan Police spokesman later attested: “Every office is accountable under law, and fully aware of the scrutiny that their actions can be held open to.

“The decision to use force is made by the individual police officer and they must account for that.”

After coming under heavy criticism and speaking out for the first time earlier this week, the Met Commissioner, Sir Paul Stephenson acknowledged the severity of the offence. He heavily condemned members of the police force who deliberately chose to hide their identity and confirmed that the results of such actions could lead to sacking.

As well as wanting officers to be more easily identifiable to the public, he also made it clear that his senior officers were to take a more robust approach in supervising the rank and file officers to ensure they could both be praised and have problem areas identified.

Speaking at New Scotland Yard Sir Paul Stephenson said: “I have made it clear consistently that uniformed officers should be identifiable and I see no reason why we should not have name tags on, when in uniform.

“I have made it absolutely clear it is totally unacceptable for any uniformed police officer not to be showing relevant identification. I have also made it clear that I will deal appropriately and proportionately with any such breach.”

He added: “If somebody is trying to deliberately avoid being identified and the reason he is doing it is so he can behave inappropriately, badly or criminally, then of course they will face the sack.”

He said the ability to identify an officer was not just an essential check on their behaviour but a way of protecting them from false allegations.

He even confirmed that he had received praise from foreign police chiefs who were “staggered” at the scale of the operation, which he called one of most challenging “in policing history” worldwide.