He said that evidence suggested another leading IS commander, Paris mastermind Abdelhamid Abaaoud, had risked travelling to England last year to vet potential suicide bombers for an attack in London.
Abaaoud was killed during a police raid in St Denis, Paris, last year.
The source said: “The key for us is Salah Abdeslam co-operating with his interrogators, which is helping unravel a deadly terror network with a wider reach than originally thought.
“They have learned that Al Qaeda style simultaneous attacks in multiple locations is the way to create maximum terror and panic.”
Meanwhile, a 25-year-old Frenchman reported to be carrying weapons and explosives for an attack in France was arrested on the Ukrainian-Polish border in May, Ukraine said yesterday.