The lethal extremist attack in Belgium has sparked a pitched debate in Britain over whether the UK would be safer if it votes to leave the European Union.

Both sides in the upcoming June 23 referendum debate claimed the attacks in Brussels strengthened their position.

Intelligence figures and senior politicians seemed divided over the security issue, with former Secret Intelligence Service chief Richard Dearlove arguing that leaving the EU would make Britain more secure. He said it would free Britain from Europe's "freedom of movement" rules and give Britain more control.

But Rob Wainwright, director of Europol, Thursday insisted that a departure from the EU would make Britain more vulnerable because it would no longer have access to intelligence-sharing systems.

The issue has also divided Prime Minister David Cameron's Cabinet.