Home Secretary Theresa May will soon announce an investigation into “unresolved questions” surrounding the collapse of the South Wales Police corruption trial in 2011.

Proceedings were abandoned after the loss of police papers relating to the murder of Lynette White in 1988. Three men had been jailed for the killing and then released before the real culprit was convicted on DNA evidence. The lost papers have since reappeared.

Throughout the White case, journalist Satish Sekar and other campaigners argued that police officers had fabricated statements and bribed and intimidated witnesses in order to fit innocent men into the frame, rather than pursue evidence pointing in a completely different direction.

Even more disturbingly, police conduct in that case appeared to be part of a wider pattern in which senior members of South Wales CID and its serious crime squad habitually conspired to subvert the criminal justice system.

In 1983, the Cardiff conspiracy and explosives trial heard detailed accounts of how police had fabricated interviews, planted evidence, deceived solicitors, sought to incriminate an MP and threatened witnesses in a concerted effort to imprison political activists on terrorism charges.

Apparently, with no substantive evidence against them but with an apparent desire to spend the rest of their lives behind bars, “guilt-ridden” suspects had blurted out confessions to their impeccably behaved interrogators.

That Cardiff jury rejected the prosecution case and acquitted all the main defendants, yet a subsequent internal police inquiry proposed no action against any of the officers involved. Indeed, some were later promoted.

In 1987, three young Cardiff men were wrongly convicted of the murder of newsagent Phillip Saunders. In this case, too, the same investigating officers and their colleagues were accused of fabricating evidence and threatening suspects.

Once again, Detective Inspector Stuart Lewis had the remarkably good fortune to hear crucial verbal admissions of guilt in the police cells — and on this occasion the jury believed him.

Only the belated introduction of taped interviews under the Police and Criminal Evidence Act finally put an end to the proliferation of unwritten or unsigned confessions in Cardiff police stations.

Defendants Michael O’Brien and Ellis Sherwood later won an unprecedented £500,000 out-of-court settlement in a civil case against Lewis and others, having served 11 years in prison for the Saunders murder. South Wales Police chiefs have always refused to apologise.

Lewis was not on the team which concocted the case against the innocent men convicted of brutally killing Lynette White, and so did not face the corruption charges brought against colleagues and senior officers with whom he had worked in the Cardiff conspiracy and newsagent investigations.

A Thames Valley Police inquiry has subsequently recorded 28 areas of complaint involving Lewis in the Saunders and other cases. It also told the usual story of lost documents, threatened witnesses, forced or fabricated statements and the other features of so many South Wales Police investigations during that period.

In 2004, Michael O’Brien’s solicitors issued a fruitless appeal for a public inquiry into gross miscarriages of justice in South Wales.

Today, Home Secretary May can make amends by ensuring that her proposed inquiry is both public and wide-ranging, going beyond the Lynette White case so that the whole cesspit of fabrication, bullying and perjury can at last be brought into the open.

That alone will ensure that all the rotten apples previously at the top of the South Wales Police barrel are held up to the light.