The family of a man who died in police custody have won their battle to stop an officer involved in the case resigning ahead of an official investigation.

Sean Rigg's relatives were outraged when the Metropolitan police accepted the PC's resignation before a new inquiry by the Independent Police Complaints Commission could formally place him under investigation.

Rigg, 40, died in 2008 after being restrained by police. The jury at his inquest condemned his treatment, saying the level of force was "unsuitable".

Now the Met has reversed its decision, hours before the Rigg family were due to go to the high court to ask a judge to injunct the police to prevent the officer from resigning. The Met announced on Friday that the officer, PC Andrew Birks, had been suspended and the acceptance of his resignation rescinded.

The decision to reverse the original decision, the Met said, was influenced by several factors including the imminent legal action by Rigg's family, and "the need for public confidence". The Met's climbdown came three hours before the Rigg family's attempt to gain an injunction was listed to be heard before a judge and the acceptance of his resignation came before the officer could be served with a formal notice that he was under investigation.

Five officers are facing investigation by the IPCC over the death. The Rigg family say they want all the officers suspended from duty, pending the investigation – the second the IPCC has launched into the death. The initial bungled IPCC investigation cleared police of wrongdoing.

But in 2012, a jury at Southwark coroners court found that police used unsuitable and unnecessary force against Rigg, with officers failing to uphold the detained man's basic rights as he collapsed after being pinned down for eight minutes.

During the restraint he was placed face down, with his legs bent back, in a caged footwell of a police van. The jury found that Rigg was struggling but was not violent and officers had failed to spot the deterioration in his health.

Rigg, 40, was a musician with paranoid schizophrenia. He was living in a south London hostel in August 2008 as his mental health deteriorated. One day he smashed up a gazebo and made karate moves that staff saw as threatening. They called the police, who did not initially respond to several pleas for help. Three hours after the first 999 call police responded, and three officers restrained Rigg.

In a statement, the Met said: "The officer requested to resign from the MPS, as is his legal right. He was not suspended, nor had he been served with legal notice that he was to be investigated by the IPCC at that point.

"However, once the IPCC informed the Metropolitan police service (MPS) they wished to serve a notice of investigation on the officer, leading them to request we review his suspension and the proposed legal action by the family of Sean Rigg, this was considered.

"This is a unique set of circumstances. In light of the public interest in this case, the need for public confidence in the accountability of police officers and in the interests of allowing a full reinvestigation to be most effectively carried out, the MPS has now suspended the officer.

"Following the suspension of the officer, the MPS has reconsidered his resignation request and the Deputy Commissioner has decided to rescind his resignation."

"The officer has given assurances, via his legal representative, that he would fully cooperate with any new investigation by the IPCC."

The IPCC said that while it could not prevent an officer leaving a force, it believed it was "unacceptable that officers can be allowed to do so and avoid the possibility of facing disciplinary proceedings".

Marcia Rigg, Sean Rigg's sister, said: "The Rigg family is relieved that the Commissioner has seen sense to suspend PC Birks and reverse his resignation, so that he can face disciplinary investigations, and possible gross misconduct charges depending on what is found.

"The Commissioner should now take the opportunity to suspend all the other key officers including the custody sergeant to ensure all comply with the independent disciplinary investigation by the IPCC. Our family now calls on the government to change the law so that other families do not have to threaten court action to stop officers resigning to avoid being held to account."