Britain's most senior counter-terror police officer has warned that social media firms are putting lives at risk by refusing to co-operate with investigations into terrorist activity.
In a speech, Metropolitan Police Assistant Commissioner Mark Rowley said some companies were designing products in such a way that they are useless to police conducting covert surveillance operations.
"Our experience of social media and communications companies is of a very fragmented and highly variable level of co-operation.
"Some refuse to assist, for some it is also a part of their strategy, they design their products in full recognition that they'll be unable to help us."