Britons benefited from pooled EU resources in the emergency response to the attack in Sousse in Tunisia two years ago, the report said

Theresa May’s Home Office drew up an unpublished document that revealed how Britons could be more at risk of terrorism and crime after Brexit.

The paper, prepared by officials with help from MI5 and MI6, warned that leaving the EU would make the UK less secure from “terrorism, criminality and illegal migration”.

Senior figures involved in compiling the document, which has been leaked to The Times, maintained that all of its fears were justified. They said it set out the details of the challenge for ministers involved in the Brexit negotiations.

The 49-page paper was produced in the run-up to the referendum last year but then dropped in a row over campaign tactics.

Mrs May oversaw the document, which started in the Home Office,