In this old unbroken democracy we've a complex relationship with our freedoms. Sometimes good fortune becomes complacency, even contempt for the liberties that others would, and did, literally, die for. Bizarrely, identical principles are viewed by some as old-fashioned heirlooms and by others as political correctness gone mad. It's as if we want to scrap the Human Rights Act and dream up a replacement according to personal taste: some want it weaker, some stronger with a flavoured syrup and skinny froth. Then reality kicks in and we go reaching for that battered bundle of protections that we hadn't quite believed people like us would ever need.

So Britain rediscovers its treasures one by one. The value of fair trials and personal privacy has become live news stories rather than history lessons. Now it is the turn of the absolute rule against torture, as today's pages reveal the full horrors of what was considered acceptable to our closest allies in the previous US Administration. And then there is the other headline issue of free speech and peaceful protest.

Dissent is the lifeblood of democracy and progress. We used to understand this. Perhaps we still do, though the revelation that Damian Green’s computer was searched for evidence of contact with me suggests otherwise. It seems our politics and policing may have become allergic to dissent.

Ofácourse there was never a golden age ofáprotest or policing and the fallout from the G20 and Ian Tomlinson's tragic death has brought back memories of many earlier controversies. Seventy-five years ago Liberty (the National Council for Civil Liberties) was formed in response to the brutal policing of hunger marches.

Indeed, there was no positive enforceable right to speech and protest in our law until the much misunderstood Human Rights Act came into force in 2000. I must concede that public order policing is a tough and thankless job and this professional protester would rather pick up a loudhailer here than in many, perhaps most, other countries.

Nonetheless, just as the new Metropolitan Commissioner has rightly decided to take concerns about the G20 policing operation seriously, the rest of us have considerable cause for reflection.áIn pursuit of a life free from irritation, offence and antisocial behaviour, have we allowed legislators to criminalise the necessary nuisance of peaceful protest too? When you attempt to control every possible human encounter, do you unwittingly infantilise police officers and protesters, robbing everyone of individualájudgment and civility?

The right to protest is precious but not unlimited. Few would argue against proportionate interferences with that right to protect people and property. Yet the past 15 years have so blurred the lines between civil, public order and anti-terror powers that we risk turning constables (whose traditional role was to keep the peace) into bouncers charged with shutting down demonstrations.

In 1994 the offence of “aggravated trespass” turned demonstrations on private land into a criminal matter, even where there was no intended harm to people or property. As we saw in the case of the Nottingham power station arrests last week, when you add the suspicion of a conspiracy to commit this offence, you create a broad discretion for pre-emptive arrests, allowing the imposition of police bail restrictions that could effectively end a time-sensitive demonstration.

In 2000 anti-terror stop-and-search laws were drawn so widely that the authorities can designate that in whole counties people can be stopped and searched without suspicion. The infamous “Section 44” power has repeatedly been used as a tool for preventing peaceful protest. Remember the elderly Walter Wolfgang at the Labour Party conference in 2005?

The Serious Organised Crime and Police Act 2005 criminalised demonstrations in and around Parliament Square that had no police permission. That December Maya Evans was convicted under the law of reading out the names of dead British soldiers at the Cenotaph. Among so very many illiberal measures, this provision has become emblematicáof liberties needlessly lost.

From the statute book to the street: police practice has built on the parliamentary trend. Coachloads of demonstrators have been contained and diverted under police escort and the tactic of kettling, or trapping large groups, often preventing their escape for hours on end, has become commonplace.áYou don't have to be a psychologistáto imagine how this informal detention without food, drink or toilet facilities might exacerbate the risks of confrontation.

This is the backdrop to the footage of Mr Tomlinson being struck by a police officer's baton. This is the mood music for the images of the argumentative but unarmed Nicky Fisher being cuffed and then beaten on the legs by a sergeant who towered above her.á

Sean O'Neill's revealing report in The Times on Thursday quoted an anonymous contributor to a police internet forum refering to Ms Fisher as a “threat”, to the unidentified sergeant as “the skipper” and to other officers as “his troops”.áPolice officers are supposed to be constables - armed with the powers of discretion and communication - as well as batons and arrest powers. Seeing themselves like the internet contributor is a recipe for conflict.

The use of force - when it is proportionate and necessary to make arrests and prevent harm to the police and public - can be reasonable. But itáis neither lawful nor productive to use violence against an individual protester, however annoying they are, because other people are misbehaving or an officer has lost his rag. As for the tactic of uniformed officers obscuring their identity numbers, the commissioner has clarified that this is unacceptable.

The G20 demonstrations may prove a momentous moment in Britain's surveillance culture.áEvery activist, journalist or passer-by with a mobile phone becomes a walking CCTV camera capable of capturing bad policing. We might all learn from this. The police will understand how it feels to be watched and the dangers of rushing from snatched images to judgment. We complainers are reminded that well-targeted surveillance has its place and that the right to privacy, like protest, is not unlimited.

Shami Chakrabarti is director of Liberty

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