The latest inquiry into one of London’s Sapphire sexual crime units makes for shocking reading. According to the Independent Police Complaints Commission, victims of rape in Southwark were pressured into retracting their complaints, in order to boost local performance statistics. Not only were the women themselves inexcusably let down. In one case, an attacker thus let off the hook went on to commit murder.

The irony is that the capital’s Sapphire programme was supposedly a sign of progress. Rape campaigners have long complained that the balance of justice is tilted away from rape victims – hence the woeful conviction rates. Part of the problem is the difficulty of establishing “beyond reasonable doubt” for an offence that often pits one person’s word against another’s. No less of an issue is encouraging traumatised victims – many of whom fear they will not be believed – to trust often insensitive institutional procedures. Specialist sexual crime units were meant to address the problem. Yet Sapphire has now been the subject of no fewer than nine investigations and appalling levels of misconduct have been revealed.

The only – slight – consolation is that Sapphire has now been fundamentally reorganised. Since 2009, all 32 local units have come under central control, and working practices have been revised. Another question remains unanswered, however. Some 19 officers have been disciplined, three dismissed and one convicted over Sapphire malpractice. But several others have escaped with nothing more serious than a slap on the wrist, despite pressure from the police watchdog for their dismissal. Two have even been promoted.

The Met claims to have learned from the failures of the past. But such assertions ring hollow indeed in the face of evidence that – once again – the police have put the protection of their own above the claims of justice. It is bad enough that so serious a crime as rape was ever treated with such contempt. That Scotland Yard apparently fails to see it that way is almost worse.