The former heads of MI5 and MI6 have warned that leaving the EU could undermine “our ability to protect ourselves” from terrorists.

Baron Evans of Weardale, the former director-general of MI5, and Sir John Sawers, the former head of MI6, say Brexit could also lead to “instability on the Continent”, compounding the current “economic difficulties, the migration crisis and a resurgent Russia”.

In an article for The Sunday Times, the former spy chiefs warn that a vote to leave could damage intelligence sharing because the EU would restrict surveillance powers if the UK were not in the union.

They write: “Intelligence work today relies on the lawful and accountable use of large data-sets to reveal the associations and activities of terrorists and cyber-attackers . The