Racism has underlain so many of the tribulations of the Metropolitan Police over the past 30 or so years that it almost beggars belief there is any left in the force to be rooted out. From the Brixton riots to Broadwater Farm to the mishandling of the Stephen Lawrence case, successive reports have identified variants of what Lord Macpherson termed "institutional racism" and demanded urgent remedial action. How far last year's London riots had directly to do with race can be disputed, but they began in Tottenham, and they followed the shooting by police of a black man and the failure of those at the local police station to respond to community concerns.

It is to the aftermath of those riots that at least one of the latest accusations about police racism appears to relate. It concerns a mobile phone recording of one officer apparently abusing a man and another officer appearing to assault a teenage boy. Those revelations prompted further questions. As of yesterday, the Met had said that 10 complaints had been made; 20 officers were being investigated by the Independent Police Complaints Commission; and eight, along with one civilian, had been suspended from duty.

While hardly a mitigating factor, it should be said that these figures are cumulative; they go back as far as 2010, and they relate to separate complaints across different parts of London. That might be the positive gloss. But the same time span and geographical spread could be interpreted more negatively as proof of the enduring and ubiquitous nature of the problem. And while the outcome of the IPCC's individual investigations must not be prejudged, the emergence of these new allegations gives cause at the very least for public concern.

The message has to be that racist attitudes are quite simply unacceptable in any police force, but doubly so in the Met, which has responsibility for policing one of the world's most ethnically diverse cities. Any hint of prejudice, any hint that some are less equal before the law than others, corrodes the trust that is essential to effective operations. Regrettably, it seems that not all of this has got through to each and every officer.

To give the new Commissioner of the Met his due, he responded to the central claim with commendable speed, condemning any manifestation of racism and doing so very publicly and with the full force of his rank. The temptation in such circumstances might be for the top brass to close ranks and blame "a few rotten apples" on the periphery. Mr Hogan-Howe did not do that. Expressing his shock, he said quite categorically: "I will not stand for any racism or racists." But it will take continued forthright leadership on his part if the scourge is to be excised. His own prominence, the greater visibility of police on London streets and the well-publicised pursuit of specific offences, such as uninsured cars, have made for a good beginning to his tenure. But there is much more to do.

In some respects, however, racism – while clearly still an issue for the Met and a key one for public confidence – is not the hardest question to address. There can be no two ways about it: racism is wrong. It is wrong in principle and in practice; a little bit racist is still racist. The cosy culture of the Met's hierarchy, on the other hand, as exposed by the Leveson Inquiry and exemplified in the links senior officers maintained with executives and journalists at News International, seems to be proving at least as hard a nut to crack. The silence from the Met on this score has been deafening. Yet the whiff of corruption has to be as corrosive of public trust as are accusations of racism, and the signs are that it reaches further up the ranks.