British interior minister Amber Rudd said on Sunday end-to-end encryption of messages offered by services like WhatsApp are "completely unacceptable" and there should be no "secret place for terrorists to communicate".
Local media have reported that shortly before launching an attack that killed four people including a policeman near Britain's parliament in central London, Khalid Masood sent an encrypted message via WhatsApp.
"That is my view - it is completely unacceptable, there should be no place for terrorists to hide. We need to make sure organisations like WhatsApp, and there are plenty of others like that, don't provide a secret place for terrorists to communicate with each other," Rudd told the BBC's Andrew Marr show.
"We need to make sure that our intelligence services have the ability to get into situations like encrypted WhatsApp."