Another draconian attempt to curb Britain's civil liberties

The attempt to prevent demonstrators from reaching Heathrow airport is the latest in a long line of erosion of civil liberties which started during Tony Blair's reign. But civil liberties groups hope Gordon Brown will mark a clear break with his predecessor by reversing the trend.

Their anger centres on the use of Section 44 of the 2000 Terrorism Act, which gives police the power to stop and search anyone in an area considered a likely terrorist target. It was used most notoriously to hold Walter Wolfgang, the veteran peace activist who heckled Jack Straw, when he was Foreign Secretary, at the 2005 Labour conference.

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In the same year, John Catt, 81, was detained as he walked towards the seafront for an anti war demonstration near the conference hall in Brighton.

He fell foul of the police after he was spotted wearing a T-shirt accusing Tony Blair and George Bush of war crimes. The police record said the "purpose" of the stop and search was "terrorism".

Protests have also been severely curtailed by the Serious Organised Crime and Police Act of 2005. Demonstrators who breach the perimeter fence of "sensitive sites" can be jailed for 51 weeks or fined £5,000 for criminal trespass under the Act.

Helen John, 68, and Sylvia Boyes, 62, both veterans of the Greenham Common protests, were the first to be arrested under the power when they walked across the sentry line at the US base at Menwith Hill, North Yorkshire. The Home Office originally designated 10 sensitive sites, including military and nuclear bases. Another 16 government buildings and royal palaces were added to the list last month.

Section 132 of the same Act requires police permission to stage demonstrations within 1km of Parliament. The provision was principally designed to silence Brian Haw, the veteran peace protester who has mounted a six-year vigil in Parliament Square. But a mistake in drafting means that Mr Haw is still in place opposite the Commons gates.

It has also been used against Maya Evans, a chef who stood on the Cenotaph in Whitehall and read out a list of soldiers killed in Iraq and against Mark Barrett, a tour guide who staged an anti-war tea party opposite the House of Commons.

After failing in the British courts, peace activists are planning to challenge the ban on spontaneous protest near Parliament in the European Court of Human Rights, arguing that it violates freedom of expression and assembly. Mr Brown has hinted, however, that the ban on demonstrations near Parliament could be overturned.

Shami Chakrabarti, the director of Liberty, said: "Speech and peaceful protest, the lifeblood of democracy, were recklessly curtailed over the last decade by one of the most authoritarian prime ministers in living memory. If our new Prime Minister wishes to turn this around, we urge a swift start."