"Can't stand Luther," says Leroy Logan, of the BBC's acclaimed detective series. "It's every stereotype you can think of. The black detective, always in trouble, always the maverick. Doesn't help."

He was Superintendent Leroy Logan a fortnight ago, probably the best known black officer in the Metropolitan police, but then his 30 years with Scotland Yard elapsed and now he is in civvies. He left with thanks from a deputy commissioner, but no exit interview. After 30 years of hands-on policing, 20 of them knee-deep in the racial complexities of policing, that seems strange. So here we are in Islington, north London – where his coppering began – and he is telling me where the bodies are buried. "The problem is cultural," he says. "If officers felt they were going to be held to account, things would be different."

It is the drift at the top and it is middle managers. "Too many sergeants are constables with stripes," he says. "They don't want to be unpopular. In terms of race, they acquiesce. They see things, hear things and do nothing. If someone is a whistleblower, they talk them out of it. They don't want to be seen as agents of change." And so, he says, the culture persists and swallows people. Bad people; good people. "During training, you would see raw recruits radicalised – there is no other word for it. They'd meet a certain kind of officer and within weeks it would change them. I'd like to think that's different now."

It's been a difficult year: a string of race misconduct cases involving police officers; a slew of senior minority officers retiring without others to fill the vacuum; a continuing failure to recruit; intractable problems with retention; and just this month, a damning report from the Independent Police Complaints Commission saying that racism complaints are still not taken seriously. Logan says he saw improvements in three decades, but not enough. "It's like a cancer. You think you've got to it and it manifests itself in a different way."

So was it a sensible way to spend 30 years? Certainly, he says. He led Hackney borough command, helped mastermind security at the Olympics and did the job he really wanted, chief inspector. "Close enough to the community but with strategic lead on things." And now he's off travelling. "I wish them well. I hope they get a grip."