Blair should go: opposition parties

But Sir Ian retained the backing of Prime Minister Gordon Brown and Home Secretary Jacqui Smith, who both said they continued to have full confidence in him.

The Metropolitan Police Authority (MPA) and Association of Chief Police Officers (Acpo) also said they supported Sir Ian and questioned the decision to bring a prosecution under health and safety legislation.

But shadow home secretary David Davis said the Commissioner's position was now "untenable".

"The trial has shed light on the serial failures that led to the tragic death of Mr de Menezes," said Mr Davis.

"They include failures of organisation, command and operations. The failures were systemic, falling within the clear responsibility of the Commissioner of the Metropolitan Police."

Liberal Democrat home affairs spokesman Nick Clegg said: "This guilty verdict makes it unavoidable that Ian Blair should take responsibility on behalf of his whole organisation and resign.

"Whilst the ruling undoubtedly raises complex questions about future police operations, the simple priority today is to show that we have a police force in London which is prepared to accept full responsibility for its actions."

And Conservative candidate for Mayor of London Boris Johnson said: "Sir Ian Blair must now consider his position. An innocent man was killed through sheer incompetence and it would be crazy if no-one carried the can."

Acpo president Ken Jones, the chief constable of Sussex Police, said the sympathies of all police officers and staff were with the de Menezes family.