A similar 'trigger' system to the one currently used by online firms to flag up child sexual exploitation should be used in the fight against terrorism, MPs have recommended.
A report released today found social media firms, most of which are based in the US, argue they do not have to comply with UK law and only are currently obliged to hand over information if it poses an "imminent threat".
It comes after an online exchange between one of Fusilier Lee Rigby's killers, Michael Adebowale, and an overseas extremist in which he set out his plan.
ITV News Correspondent Juliet Bremner 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