I felt a profound sense of frustration when I read Saturday's Guardian account of another "police racism" allegation against the Metropolitan police. The circumstances of the case, in which an officer is apparently recorded racially abusing a man he's just arrested – are still the subject of investigation. But as someone who spent most of his adult life in policing, two issues are as plain as a pikestaff. First, yet again, there seems to have been an almost total absence of leadership and supervision of junior officers; second, the impact on "real" policing will be profound.

Last Thursday, in Tottenham, I gave the 2012 Bernie Grant Memorial Lecture. To an audience still shell-shocked by the damage to their homes and livelihoods wrought by the riots and failure of policing last August, my theme was the urgent need for the police, particularly in urban communities, to rediscover a service ethos that had been sacrificed on the altar of so-called management efficiency over the past 15 years. In any liberal democracy, policing must be by consent, and you lose that consent immediately if you alienate the community and treat them as the enemy.

Confrontational – yet frightened and defensive – officers are nowadays trained to see the public as a threat to their very existence. Preventive patrolling has been abandoned – notwithstanding the soothing and wholly false spin of the Met, which continually we still have "bobbies on the beat". Few such officers have been deployed for at least 10 years, and their barely visible replacement – comprised largely of police community support officers, are but a pale imitation of what people expect and deserve.

From Stephen Lawrence to Mark Duggan; from the kettling of peaceful protesters, to the riots of last year; from the manifest incompetence of the first phone-hacking inquiry to allegations of corruption at the Leveson inquiry – a path has been beaten towards the edge of a precipice, and it is time for those concerned about the vital role of policing to challenge what is happening.

In some respects we only have ourselves to blame. People too often accept what they are told by police leaders and politicians, and seldom demand policing be accountable at all times and at every level of interaction. Senior officers continually tell us policing is a complex, dangerous occupation, requiring an almost priest-like sense of vocation and superhuman courage. Hence the pseudo-military terminology applied to most activity, with reference to the "frontline", as if officers spent all their working hours in an environment comparable to the first world war trenches.

But what is missing from an environment where the police regard themselves almost as an army of occupation is any sense of community, any sense that they are part of us. This fundamental attitudinal change is a comparatively recent feature of policing and has undermined the trusted model of policing in our communities developed over many decades. Something has to change – and quickly.

For what is beyond doubt is that the people who suffer most at the hands of drug-dealers, knife crime and "gangsta" gunmen are those at the bottom of the social pyramid. Most are decent people who just want to work, bring up their children, and live their lives unmolested; yet they are regarded by the police as a dangerous underclass who can only be dealt with aggressively.

What incentive will there be for any black British mother on a sink estate to search out her local police to express concern about her son or his friends? Who can be surprised at any hard-working black member of our society taking the view that an organisation that allegedly views him or her as a "n****r" isn't worth their trust? I hope the Met commissioner has this incident at the top of his agenda as his management board meets on Monday.

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