The trial of a confessed killer cleared of murdering an alleged robber was a “serious miscarriage of justice” according to a former member of the London Criminal Justice Board.

Lee Jasper, a former senior policy advisor to the Mayor of London, has called for an investigation into the trial of Samuel Quamina, 49, after a jury decided he lawfully killed Perry Nelson Junior, 24.

Croydon Crown Court heard last week Mr Nelson had been part of a botched robbery at Mr Quamina’s flat in Peckham. But Mr Nelson’s guilt has never been established.

Doubts have been raised by the family and friends about the true purpose of his visit.

During the trial, the court heard the alleged robbers, including Mr Nelson, rushed into Mr Quamina’s house, armed with a pistol and a car steering lock.

Mr Quamina told police that, fearing for his life, he stabbed and slashed at the robbers, fatally injuring Mr Nelson and stabbing another man in the back.

But campaigners claimed no evidence was presented to prove robbery was the motive.

Three other men have yet to stand trial for the alleged robbery.

Mr Jasper said: “This case is outrageous. The Crown Prosecution Service and the Metropolitan Police Service undermined their own prosecution.

“The assumption was a robbery took place and that is why Mr Nelson attended the property, when in fact there is no evidence to suggest this.”

Now Mr Jasper, along with Donna Nelson, Perry’s mother, want a Police Complaints Commission inquiry into the police investigation and in the process of making an official complaint.

Mrs Nelson said: “I am not trying to say my son was an angel but he was a clever and intelligent man who would not have got himself involved in something like this.

“He was about to start a lucrative business venture and comes from a loving family and was talking about starting one of his own with his fiancee.

“I don’t believe this case was thoroughly investigated and my son was automatically assumed to be guilty of robbery.”

Mr Jasper said: “We call on the Crown Prosecution Service and the Metropolitan Police Service to investigate what could potentially be a serious case of miscarriage of justice.”

The family also wants police to re-examine the case after it emerged police did not visit Mr Quamina’s flat until the evening after the death and Mr Quamina’s violent criminal past was withheld from the jury.

A CPS spokeswoman said: “The Crown applied to adduce Quamina’s previous convictions, but the judge ruled that they were not admissible.

“The available evidence pointed to this being a robbery.

“This was supported by Mr Quamina’s statement, and it was that statement which meant he was standing trial at all.

“The men who attended the flat – the robbers – had lied to police throughout about what happened and why they were there, they could only have been called as witnesses had they pleaded to the robbery charge.”

A police spokeswoman refused to comment.