The father of Fusilier Lee Rigby has said he wants an apology from Britain's intelligence services after accusing them of failing to prevent his son's murder.
The Intelligence and Security Committee said in a report that spy agencies could not have stopped the soldier's murder in May 2013, despite his killers featuring in a total of seven error-filled operations before the attack.
Internet firms need to act to prevent terrorists from plotting "murder and mayhem" on their networks, the Prime Minister has argued.
David Cameron made the comments after the release of a report by the government's Intelligence and Security Committee, which raised concerns over some social media companys' policies when it came to tackling suspicious behaviour online.
ITV News UK editor Rohit Kachroo reports:
Lee Rigby's stepdad and sister criticised social media companies for failing to notify the authorities of users plotting a terror attack.
ITV's UK Editor Rohit Kachroo looks at the findings of a report into the extent of intelligence agencies' knowledge of Lee Rigby's killers