The Intelligence and Security Committee (ISC) has said that US tech companies should open themselves up to British intelligence services to avoid future terrorist attacks, in a recommendation that has been blasted by privacy groups.

While the ISC mostly backed away from criticising MI5 over its failure to prevent the murder of Lee Rigby, it said that if internet companies had acted more quickly the attack could have been avoided.

The report criticised one company in particular for not having flagged up a conversation where Michael Adebowale told someone else to kill a soldier. It did not publicly name the company, which some reports said was Facebook. Facebook did not comment.

“The party which could have made a difference was the company on whose platform the exchange took place,” the report said. “However, this company does not appear to regard itself as under any obligation to ensure that its systems identify such exchanges, or to take action or notify the authorities when its communications services appear to be used by terrorists.”

It also went on to criticise other US tech giants such as Facebook, Apple, Google, Microsoft, Twitter and Yahoo more generally, for the ‘considerable difficulty’ that British intelligence agencies have found in accessing their content.

But privacy groups said that the ISC was using the situation to provide a justification for spying.

“The ISC is spinning the facts in an attempt to condemn US technology companies for not spying on their customers,” said Eric King, deputy director of Privacy International, the UK-based right to privacy charity. “Law enforcement should have powers to intercept and acquire communications when necessary, but deputising private companies to do it for them is not the right answer.

“It is not appropriate for internet services — who handle some of our most private and sensitive correspondence — to be snooping through that data for the police, anymore than it would be for the postman to snoop through peoples' letters.”

The ISC’s criticism echoes the opinions of GCHQ’s new director, Robert Hannigan, who wrote early this month that the internet has become the “a terrorist’s command-and-control network of choice”, in a piece for the Financial Times.

“However much they may dislike it, they have become the command-and-control networks of choice for terrorists and criminals, who find their services as transformational as the rest of us,” he wrote. “If they are to meet this challenge, it means coming up with better arrangements for facilitating lawful investigation by security and law enforcement agencies than we have now.”