Google, Facebook and other big internet companies will be forced to hand over encrypted conversations of suspected terrorists and criminals under plans to bolster surveillance powers in Britain.
New laws will require applications to hand messages sent by their users to MI5, MI6 and GCHQ if they are under investigation.
The power will be included in an Investigatory Powers Bill which will overhaul the spy agencies' ability to monitor suspects.
The Bill, announced in the Queen's Speech, will revive the so-called "snoopers' charter" but is much wider than previously planned.
The Conservatives are pushing ahead with legislation blocked by the Liberal Democrats. The Government has promised to "address ongoing capability gaps" that it says hinder the ability of the security services to fight terrorism and other serious crime.
It will also seek to allow the intelligence agencies to "target" the communications of terrorists, paedophiles and serious criminals.
The Tories said they would also push ahead with plans to allow Ofcom to take "tough measures" against broadcasters that air interviews with extremists.
Schools, nurseries and organisations working with children will be able to check whether a potential member of staff is an extremist.
The security and intelligence agencies are concerned that the encryption of conversations is now so sophisticated that they cannot discover what suspects are planning.
The proposed powers would allow spy agencies to obtain a warrant from the Home Secretary obliging an internet company to break down its encryption protection and allow access to a suspect's communications.