UK spy agencies want to install 'black box' surveillance devices across the country's communications networks to monitor internet use, it emerged today.

A report by an influential committee of MPs tells how spooks are keen to implement a nationwide surveillance regime aimed at logging nearly everything Britons do and say online.

The spy network will rely on a technology known as Deep Packet Inspection to log data from communications ranging from online services like Facebook and Twitter, Skype calls with family members and visits to pornographic websites.

But civil liberties and privacy campaigners have reacted with outrage, saying that the technology will give the government a greater surveillance capability than has ever been seen.

The report by Parliament's Intelligence and Security Committee, published on Tuesday, gives UK intelligence agencies' perspective on the government's draft Communications Data Bill, which is intended to update surveillance powers.

The government argues that swift access to communications data is critical to the fight against terrorism and other high-level crime, but it has been delayed after the Liberal Democrats dropped support for the bill. 

MI5 chief Jonathan Evans told the committee: 'Access to communications data of one sort or another is very important indeed. It’s part of the backbone of the way in which we would approach investigations.

'I think I would be accurate in saying there are no significant investigations that we undertake across the service that don’t use communications data because of its ability to tell you the who and the when and the where of your target’s activities.'