Being part of the EU does "little to keep Britain safe" against terrorists and regaining border control would be a "valuable defensive tool", a minister has claimed.
Brexit campaigner Dominic Raab said EU rules on free movement "force us to import risk into the UK".
The Justice Minister raised fears about UK security during a speech called Brexit and Security: The Case for Operational Cooperation, Without Sacrificing Democratic Control, in London on Wednesday.
The Eurosceptic Tory MP for Esher and Walton told Vote Leave supporters that "being a member of the EU does little to keep Britain safe that we couldn't achieve outside".
He also said that UK intelligence agencies are powerless to bar EU nationals believed to be linked to terrorism from entering the UK.
"We cannot refuse entry to EU citizens producing an EU passport, even though we have no control over the checks made by the country of issue, which we can charitably say are of mixed reliability," he said.
Under the Free Movement directive, EU member states can only deny entry to EU nationals where they present a "genuine, present and sufficiently serious risk".
Mr Raab said UK intelligence agencies cannot bar individuals on "whom we have sketchy intelligence" but have reason to believe they may be linked to terrorist related or serious criminal activity - or those who may have travelled to Syria without clear reason.
He added: "In most countries outside the EU, you can bet individuals flagged in this way would not waltz through passport control without these doubts or question marks being answered.
"EU rules set the bar for taking meaningful action impossibly high, which means we effectively have to give a free pass into Britain to those coming from the EU who may pose a threat."
He said this "massively increases" the number of people that have to be monitored by intelligence agencies - making it harder for them to sift out those who present a serious risk.
"That means we are importing risk and stretching our capacity to cope with it on frankly a pretty worrying scale," Mr Raab added.
Referencing Home Office figures - citing the 6,000 EU nationals that were turned away at the border, in contrast to the 67,000 non-EU nationals - he said Brexit would "result in stronger preventative checks."
"It is undeniable that regaining control over our borders would be a valuable defensive tool in protecting Britain from future terrorist attacks," he added.
Mr Raab also said that the money saved from withdrawing, using the net contribution of around £10 billion last year, would "almost double the budget" for every UK police force.
He added that the new draft Regulation for Europol will do "nothing to boost the intelligence or counter-terrorism capacity in any member state," and is merely obsessed with "strengthening Europol's independent legal status".