Chris Phillips, former head of the National Counter-Terrorism Security Office, said he is “convinced” that a terror attack will take place at “some stage”.

The plot to kill Theresa May was said to the ninth terrorist plot foiled since March, sparking Mr Phillips fears of another deadly attack in Britain.

According to reports, one man was plotting to blow up the security gates at Downing Street with an explosive hidden in a bag.

The man then allegedly planned to storm Number 10 armed with a knife and suicide vest to kill the Prime Minister.

A man, 20, has been charged with preparing acts of terrorism and is understood to have been arrested by the Met Police last week.

A 21-year-old man is accused of assisting him.

Speaking to talkRADIO, Mr Phillips said: “I really think we’re going to have a spectacular terrorist attack at some stage where hundreds may even thousands of people are injured.”

He added “the intention was to have three large vehicle bombs” in Barcelona and something like that happens “then you get thousands of people killed and injured”.

Mr Phillips concluded: “I’m convinced we’re going to see that at some stage.

“Let’s think about this now and do something now whilst we’re not in that position.

“It needs some brave governments to come up with some control orders or something much stricter than we’ve got at the moment that does put people who are concerning under much tighter guidelines.

“That’s not being done at the moment, in fact, the Conservatives watered down the control orders… and that’s rubbish, they are absolutely rubbish.

“I would consider that we need to do something about those people that’ we’re really scared of but have not yet committed offences.”