National security takes centre stage in European Union referendum campaign
The rival sides in the European Union debate have clashed over the potential impact of Brexit on national security as the referendum campaign stepped up in intensity.
Two former spy chiefs argued that Brexit could hamper the UK's ability to protect against terrorism and David Cameron is set to make the issue a central theme of a major speech on the EU on Monday.
But Justice Secretary and Vote Leave campaigner Michael Gove said the country could take "immediate steps to make this country safer" if the country quits the EU on June 23.
Lord Evans of Weardale, the former director general of MI5, and ex-MI6 chief Sir John Sawers, said the UK benefited from the exchange of information with other EU countries.
Writing in The Sunday Times, the ex-spies said: "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 terms on which we exchange data with other European countries are set by agreement within the EU.
"As an EU member, we shape the debate, we push for what we think is the right balance between security and privacy and we benefit from the data that flows as a result."
They warned that "an agreement reached without us would probably be too restrictive for our needs" and "could undermine our ability to protect ourselves".
Sir John told BBC One's The Andrew Marr Show: "It's not just about the day-to-day co-operation, it's about the wider stability of our continent. We are only secure because the wider Europe is secure.
"Pulling out will make it more dangerous. There is a real risk of the pressures on the European Union - migration pressure, economic pressures, pressures from Russia - pulling the European Union apart.
"We are seeing politics in Europe going to the extreme left, to the extreme right. We need to make sure that the centre is solid and the European Union plays its role underpinning democracy, human rights and the rule of law in Europe."
But Mr Gove said Europe "needs to think again" and insisted the country would be safer outside the EU.
He dismissed the warnings from Sir John, highlighting that other experts including former MI6 chief Sir Richard Dearlove and ex-Interpol boss Ron Noble had issued warnings about the EU's "open borders" policy.
Mr Gove said: "I have enormous respect for Sir John and his tradition of public service, but he is flat wrong."
He added: "I'm the Justice Secretary, I know that the European criminal records information system (Ecris) doesn't allow us to know whether or not criminals come into this country.
"We only find out whether or not people have criminal records after they have already committed an offence in this country. It is a gossamer-thin protection."
The UK's most valuable intelligence-sharing deal was with the Five Eyes group of the US, Canada, Australia and New Zealand.
"Within the EU, intelligence sharing doesn't work effectively," he said.
He told The Andrew Marr Show: "Why are they going wrong? They are going wrong because of Schengen, the open borders deal which was a big mistake and they are going wrong because of the euro, the single currency, which is a big mistake.
"The two biggest projects of European integration over the last 10 years have been bad for the continent and bad for its citizens.
"Europe needs to think again and we can make it think again by showing how greater democratic control is in everyone's interests."
He proposed emergency laws as soon as possible after the June 23 referendum to take the UK out of the jurisdiction of the European Court of Justice.
The plans would exempt the intelligence agencies from EU law, ending the application of the Charter of Fundamental Rights to the UK and measures to allow the deportation of EU citizens whose presence is not conducive to the public good.
The plans would also exempt the Armed Forces from the scope of EU law and end t ax refunds to big business, potentially saving between £7.2 billion and £42.9 billion by 2020-21 according to Vote Leave.
On Monday both Mr Cameron and Brexit-backing Boris Johnson will make major speeches as the referendum campaign begins in earnest following the "Super Thursday" elections last week.
The Prime Minister will make the "big, bold patriotic case" for a Remain vote, insisting that membership of the EU strengthen's the country's influence on the world stage.
Mr Cameron will say: " I want to show that if you love this country, if you want to keep it strong in the world, and keep our people safe, our membership of the EU is one of the tools - one of the tools - that helps us do these things, like our membership of other international bodies like Nato or the UN Security Council.
"And I have just one yardstick: how best do we advance our national interest?
"Keeping our people safe at home and abroad, and moulding the world in the way that we want - more peaceful, more stable, more free, with the arteries of commerce and trade flowing freely.
"That is our national interest in a nutshell - and the question that has confronted every British prime minister since the office was created is: how best to advance Britain's interests in the circumstances of the day?
"If my experience as Prime Minister had taught me that our membership of the EU was holding Britain back or undermining our global influence, I would not hesitate to recommend we should leave.
"But my experience is the opposite.
"The reason I want Britain to stay in a reformed EU is in part because of my experience over the last six years is that it does help make our country better off, safer and stronger."