EU referendum: Are we safer in or out of Europe?

The Paris and Brussels attacks put national security at the heart of the EU referendum debate.

Outers such as Nigel Farage were quick to point to Britain's 'porous borders' as a consequence of EU membership, claiming it puts British nationals at risk.

Meanwhile those in favour of staying in the EU accused Mr Farage and others of scaremongering and said that Britain's security is enhanced by working with other European countries.

The key arguments of those wanting to leave are that being in the EU makes it easier for terrorists to come to the UK, supremacy of EU courts makes it harder to deport violent criminals, and that Britain would still co-operate with other European countries to fight terrorism after Brexit, as currently happens with the US.

While the other side argues that Britain does not have open borders because it still requires passport checks as it is not in the Schengen area, Europol membership allows the UK to share intelligence and fight cross-border crime, and that the European Arrest Warrant has returned more than 1,000 criminals to face justice in the UK.

Common justice and security policies were never part of the original European plan.

Yet as the EU has grown and developed, so has its role in security.

All airlines are now forced to provide passenger information to all member states, the EU is building a system so each country's police can search for DNA, fingerprint and vehicle matches on another nation's database. And there is an EU immigration intelligence system.

Europol, the body that co-ordinates policing and security, works on counter-terrorism planning, combating online extremism and people smuggling.

Frontex, the EU's border security agency, runs operations to identify and manage migrants across the Mediterranean. Another body, Eurojust, works on measures to improve co-operation between prosecutors to ensure cross-border criminals face trial.

But what does it not do?

There is no EU spy agency and there is no EU police force – yet. The EU has a vision for an 'ever-closer' union.

Each nation has its own legal systems. For instance, the EU has been trying to come up with measures to combat illegal firearms – but the nations have wildly different gun laws.

The UK's strongest security relationship is with the United States, followed by Australia, Canada and New Zealand – although the agencies also work very closely with key European powers.

European countries also have a poor record on intelligence-sharing, combined with its thinly-policed internal borders, could mean a terrorist could reach the UK via Europe.

But even there experts are split. Security and intelligence chiefs have backed both sides.

Former MI6 boss Sir John Sawers 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.

"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."