The European Court of Human Rights upheld a complaint on Tuesday against a British anti-terrorism law that allows police officers to search individuals without firm grounds for suspicion.

The judgement backed two British citizens who were stopped and searched at a demonstration near an arms fair in London in 2003, saying the fact that officers could act on simple intuition left too much discretion to police.

Under a law passed in 2000, police can issue an order for anyone to be stopped and searched without reasonable suspicion of wrongdoing if it is judged "expedient for the prevention of acts of terrorism."

The court said in a statement there was "a clear risk of arbitrariness in granting such broad discretion to the police officer."

It also said the use of the coercive powers to require an individual to submit to a detailed search of their person and belongings "amounted to a clear interference with the right to respect for private life."

British policing and security minister David Hanson said the government would seek to appeal the decision and the powers would remain available to police pending the appeal outcome.

"Stop and search under section 44 of the Terrorism Act 2000 is an important tool in a package of measures in the on-going fight against terrorism," he said in a statement. "I am disappointed with the ECHR ruling in this case as we won all other challenges in the UK courts."

In 2006 the House of Lords, then the highest appeal court in the United Kingdom, unanimously dismissed the applicant's appeal, questioning whether a superficial search of a person could be said to show a lack of respect for their private life.

In response to the ECHR's ruling, human rights group Amnesty International called on the government to scrap the powers.

"These police powers ... clearly violate people's right to privacy and family life," said Halya Gowan of Amnesty International's Europe and Central Asia Programme.

"These powers also contravene the rights to liberty, freedom of expression and assembly, and freedom from arbitrary detention, all of which the UK is bound to uphold."

Tuesday's judgement is the latest in a series against British anti-terrorism laws.

In February 2009, the court ruled that Britain had acted illegally in detaining nine men under an anti-terrorism law passed after the September 11, 2001 attacks in the United States.

It has also ruled several times against laws passed during the conflict in Northern Ireland.