Britain has seen several violent attacks by Islamist-inspired extremists in the past two decades. The deadliest was on July 7, 2005, when four suicide bombers killed 52 commuters on London subway trains and a bus.
More recent knife and vehicle attacks have largely been the work of individuals inspired by militants such as the Islamic State group, but not directed by them.
McCallum said U.K. authorities had disrupted 31 attack plots in the past four years, by both Islamic and far-right extremists. He said it was hard to say whether Britain was safer or less safe, 20 years after the Sept. 11 attacks in the United States.
“The number of plots that we disrupt nowadays are actually higher than the number of plots that were coming at us after 9/11, but on average they are smaller plots of lower sophistication,” he said.