Ever since the devastating quadruple bombing of London’s transport system on July 7 2005, there has been an overarching unanswered question: why was the ringleader, Mohammad Siddique Khan, not apprehended even though he crossed the radar of the Security Service and the police eight times?

This week, parliament’s intelligence and security committee finally concluded MI5 was under­resourced and overstretched. That is a fair but incomplete answer.