The police officer questioned over the death of a news vendor during the G20 protests should not have been in the force.

He had retired from the Metropolitan Police with an unresolved disciplinary charge but vetting blunders allowed him to return.

Ian Tomlinson, 47, died after he was hit and pushed by the officer during the G20 protests in April. The policeman has been questioned as part of a manslaughter investigation.

The officer retired sick after a road accident when he was accused of using unnecessary force against a driver. However, he was able to join Surrey Police, and later transfer to the Metropolitan force because the unresolved disciplinary issue was not flagged up during vetting. The Independent Police Complaints Commission would not comment yesterday.

Scotland Yard said it was cooperating with the IPCC.

Denis O’Connor, Her Majesty’s Chief Inspector of Constabulary, is expected to publish his preliminary findings on the operation this week.

Scotland Yard ordered a review of public order policing after mounting concerns of the tactics employed by police at the G20 protests. Sir Paul Stephenson, Metropolitan Police Commissioner, called in Mr O’Connor, to lead the review of public order policing.

Last week the Commons Home Affairs Select Committee published a highly criticial report on the policing of the protests.

It found that inexperienced and inadequately trained police officers were pitched into the middle of the “highly combustible” G20 protests.

The Metropolitan Police was accused of presiding over a breakdown of communications, heavy-handed use of the crowd-containment tactic of “kettling”, and creating a “them and us” attitude to protesters.

The report said that many officers policing the protests received only two days’ training each year in public order techniques. “It is troubling that the policing operation relied so heavily on untrained, inexperienced officers,” the report said.

The report did not comment on the death of Mr Tomlinson, the newspaper vendor, or the case of Nicola Fisher, who was struck across the face by a police sergeant.

But the MPs said that the images and film footage of those incidents shocked the public and have the potential to undermine trust in the police. They hoped the incidents would mark the start of a widespread debate on the use of force by the police.

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