Leading article: Petty excesses that add up to a major assault on our freedom

It is 15 February 2003. One million people or more are pouring on to the streets of London in a last effort to avert the imminent invasion of Iraq. The Prime Minister is addressing the Labour Party's spring conference in Glasgow. Alluding to the huge protest, Mr Blair said this: "I rejoice that we live in a country where peaceful protest is a natural part of our democratic process."

These were admirable and proud words - words that every citizen of this country - for or against that war - would surely have endorsed. If we had only known then what we know now, we might have called for them to be engraved in stone, with their attribution, and positioned on the wrought iron gates at the entrance to Downing Street. Lest we, or the occupant of No 10, forget.

How long ago those days suddenly seem from the perspective of this week. On Wednesday, a 25-year-old woman, Maya Evans, became the first person to be convicted under a new law that makes it illegal to stage an unauthorised protest within 1km of Parliament Square. Read those words again, slowly. Is this really Britain? The whole concept of a law against unauthorised protest close to the national parliament is something we associate with repressive states - places like China or Uzbekistan, say - not with our own long-established democracy.

To warrant arrest, then, Ms Evans must have been engaged in some highly disruptive activity. In fact, she and a companion were standing outside the fortress that is now Downing Street, reading aloud the names of British soldiers who have died in Iraq. Her companion, who had spoken to the police in advance, was released without charge. Ms Evans was found guilty, given a conditional discharge and ordered to pay costs.

Now, it could be argued that, in the context of the new law - Section 132 of the Serious Organised Crime and Police Act 2005 - she got off lightly. Section 132 envisages a fine up to £1,000. The fault lies less in the conviction than in the law. Protesting peacefully within shouting distance of the institutions of power should be a universal right in a democracy. Whitehall and Parliament Square are made for the purpose. Whose public spaces are these, anyway?

The intention of the legislation was apparently to evict the long-standing peace protester in Parliament Square, Brian Haw. In a poetic twist, however, the law may not be applied retrospectively - a view upheld when Mr Haw was briefly arrested yesterday, after police apprehended a visitor to his encampment. So Mr Haw remains, to be harassed over any new arrival - and Ms Evans pays. The law has its uses, if not the precise use for which it was conceived.

Section 132 is not the only piece of legislation to have found a dubious new application. Remember the ejection of 82-year-old Walter Wolfgang from the Labour conference after he to heckled Jack Straw? This was under Section 44 of the Terrorism Act, a provision increasingly used to intercept people who formerly would have been regarded as common or garden protesters.

Today is Human Rights Day. British and US anti-war protesters, led by Rose Gentle and Cindy Sheehan - who both turned to campaigning after losing sons in Iraq - are holding a conference in London. They plan to visit Mr Haw at his camp. Are the police even now out with their tape, measuring the 1km in a straight line from Parliament Square beyond which they may not advance without authorisation?

Petty and absurd though they seem, such small excesses add up to a serious assault on our rights. This is how freedom starts to shrink. Now who was it again who described peaceful protest as "a natural part of our democratic process"?