Edward Snowden said  the Investigatory Powers Act – which the UK parliament passed last year and which he described as “the most extreme surveillance law in the history of the western world” – was being justified as a means of rooting out terrorists.

Snowden said he understood the move, but added that there is no public evidence that these policies are effective. On the contrary, there is clear evidence that they cause harm to the public, he said.

“We have seen people fall on blacklists. We have seen, again and again throughout history, political parties be hamstrung, to face resistance, be silenced by governments because of their politics, their beliefs, their ideologies, which over time are always derived from what state security agencies say is a necessary effort to protect the nation.”