Islamic State jihadists in the European Union (EU) are able to get hold of automatic rifles thanks to a loophole in the law.

A European Union-wide crackdown on illegal firearms after the terror attacks in Paris failed to include the types of weapon often used by terrorists because EU law does not include so-called “acoustic expansion weapons”.

These are often sold to film makers as props and are classified as blank firing rather than deactivated firearms, however they have been obtained by terrorists and converted to fire live rounds. Police believe these are precisely the class of weapons used in the Charlie Hebdo attacks, and that similar weapons will likely be found in the homes of the Brussels attackers.

It is believed many of these guns originate in Eastern Europe, with focus turning to Slovakia in particular. Sources told The Times that thousands may already be in the hands of criminal gangs across the continent, yet they remain legal under EU law.

The revelations will likely fuel the debate over whether Britain really is more secure within the European Union. The European Commission is under increasing pressure to close the loophole, but progress is slow and the European Parliament is not set to debate the issue until September.

A Commission spokesman confirmed that the EU’s firearms directive did not include blank firing acoustic weapons or so-called “alarm weapons” such as starter pistols and flare guns, which can also be converted to fire live rounds.

Last month, the lead singer of Eagles of Death Metal, who were playing at the Bataclan theatre in Paris when gunmen opened fire, said the massacre may not have happened if everyone had been carrying guns.

Jesse Hughes said France’s strict gun control laws were useless in stopping the attack. “I think the only thing that stopped it was some of the bravest men that I’ve ever seen in my life charging head first into the face of death with their firearms,” he said.

“I know people will disagree with me… but that night guns made them equal and I hate it that it’s that way… Until nobody has guns everybody has to have them.”