The police have always faced a degree of suspicion from the public. The founders of the Met dressed their men in blue rather than the more military red to underline their civilian role. Keeping the peace is one of society's toughest jobs and one that our police have performed sometimes successfully, sometimes not.

Unfortunately, the events of the past week will be remembered as a low point. The arrest, early on Monday, of 114 demonstrators in a school outside Nottingham on suspicion of conspiracy to cause criminal damage and aggravated trespass, long before they managed to get anywhere near the Ratcliffe-on-Soar coal-fired power station, smacked of intimidation; the bail restrictions then placed on them draconian and deeply unsettling in a free society. The investigation into leaks at the Home Office that led to the arrest of Damian Green appears to have gone far beyond remit, with officers fishing for emails to Shami Chakrabarti, director of Liberty.

And news that Ian Tomlinson, the news-paper vendor shoved to the ground during G20, died of internal bleeding rather than a heart attack, is shocking. If all this wasn't enough, there is a wealth of video evidence online showing excessive force being used against demonstrators. Yet it's increasingly clear we cannot trust the police account of events. The Met has dodged, denied and delayed its response to questions over its conduct.

Chakrabarti acknowledges that "public order policing is a tough and thankless job". That is indisputable, but to succeed the police must have the trust of the public. It shows just how far we are from that ideal when officers are being spotted at demonstrations with their ID tags deliberately obscured. No police force should tolerate such brutish arrogance.

This aggression is no doubt linked to the government's nasty habit of writing laws that prefer the convenience of security forces to the rights of free citizens. But the police are public servants, not government enforcers. Their job is to keep the peace, not clear the streets of dissent.