Quitting the European Union would put peace and stability at risk and hamper the fight against terror, David Cameron has warned, as he made the “patriotic case” for a Remain vote.
The Prime Minister also insisted there is “safety in numbers” as he argued that staying in the 28-member bloc was crucial in the fight against Islamic State (IS).
Leave campaigners have had years to work out what would happen after a Brexit, but have failed to do so, he said.
In a speech at the British Museum, he warned that quitting was a reckless and irresponsible economic risk.
But Mr Cameron turned his focus on the impact that quitting would have on Britain’s safety and international standing.
The UK must be strong in Europe if it wants to be strong in the world, the Prime Minister insisted, as he praised the EU for reconciling warring countries.
Mr Cameron said: “The serried rows of white headstones in lovingly-tended Commonwealth war cemeteries stand as silent testament to the price this country has paid to help restore peace and order in Europe.
“Can we be so sure that peace and stability on our continent are assured beyond any shadow of doubt?
“Is that a risk worth taking?
“I would never be so rash as to make that assumption.”
Mr Cameron said the referendum would decide the “destiny” of the country and would have “real, permanent and direct consequences” for everyone in the UK.
The PM said he understood why some voters’ “heads and hearts are torn” but insisted “despite its faults” Britain was better off in.
Mr Cameron said he would “not hesitate” to have recommended that Britain quit if he had found it was being held back but he had found the “opposite”.
Britain’s membership of the EU “amplifies” its power in the world, he insisted.
The rise of a “newly belligerent” Russia, the fight against IS, also known as Daesh, and the migration crisis require “unity of purpose” and underlines the need for co-operation, he said.
Nato remains the “cornerstone” of national defence and “top military opinion” is clear that the EU is a “vital” reinforcement to the organisation, the PM added.
Mr Cameron attacked those who want the EU to collapse and claimed if Britain triggered such a move it would be an “act of supreme irresponsibility”.
“Now is a time for strength in numbers. Now is the worst possible time for Britain to put that at risk. Only our adversaries will benefit.”
Warnings by two former spy chiefs – Lord Evans of Weardale, former director-general of MI5, and ex-MI6 chief Sir John Sawers – that Brexit could harm the country’s ability to fight terrorism was “unmistakable”.
The Paris and Brussels attacks were a reminder that “we face this threat together and will only succeed in overcoming it by working much more closely together”.
Mr Cameron insisted border controls were not enough in the fight against terror.
“It takes a network to defeat a network and European measures are a key weapon,” he said.
“I don’t argue that if we left we would lose any ability to co-operate with our neighbours on a bilateral basis, or even potentially through some EU mechanisms.
“But it’s clear that leaving the EU would make co-operation more legally complex and make our access to vital information much slower and more difficult,” he said.
Mr Cameron said membership of the EU “magnifies” Britain’s power.
During its membership of the bloc, the UK has taken foreign and defence policy decisions “in our own interests”, including “liberating the Falkland Islands in a great feat of military endeavour”, freeing Kuwait from Iraq and the mission in Afghanistan.
The Prime Minister said: “The idea that the EU has emasculated our power as a nation, this is complete nonsense.”
Asked why he called the referendum if the consequences of the UK leaving could be as dangerous for the world as he claimed, Mr Cameron said: “I think it’s right to have the referendum. This is a great act of sovereignty for the British people, that’s a great act of democracy. I have always believed we are better off in a reformed EU.”
The Prime Minister denied that the open warfare among Cabinet ministers over the issue would make it impossible for them to work together again.
“We are working in Cabinet today,” Mr Cameron said, as he defended the move to allow ministers to speak against Government policy on EU membership. “It is an unprecedented act for 40 years, but it is the right thing to do.”
The Prime Minister rejected claims he was “crying wolf” over the dangers of war as he insisted genocide in the Balkans in the 1990s was “a fact”, though he insisted the EU alone was not responsible for general peace on the continent in the past 70 years.
Dutch ambassador Simon Smits provoked laughter when he congratulated the Prime Minister on his address, and joked that Boris Johnson was “already sharpening his bicycle spokes to stick in your arguments”.
Armed Forces Minister Penny Mordaunt, who is campaigning for Brexit, rejected the claim that leaving the EU would heighten the risk of war.
“The Prime Minister today is trying to tap into a vision, which I think we all share, of nations living in peace,” she told the BBC Radio 4 Today programme.
“What is being debated though is (whether) the EU is necessary to that and I would actually argue that its current trajectory is absolutely counter to that.
“At the same time he is telling us that we are heading for war if we leave, the EU is denying us the tools we need to protect our own citizens.”