For the intelligence and security officials charged with the task of keeping Britain safe from terror attacks, it was simply a question of time before a lone fanatic brought carnage to the nation's streets.
Politicians, the police and intelligence chiefs have been warning for months that Britain faced the imminent threat of attack following the recent wave of atrocities committed in European capitals such as Paris, Brussels, Berlin and Istanbul.
And, with Islamist terror groups such as al-Qaeda and Isis (Islamic State) showing no sign of abandoning their commitment to attacking the West, Britain's security forces have been in a state of high readiness in anticipation of such an attack.
Compared with other European cities, London has, until yesterday, escaped relatively unscathed from the growing menace posed by Islamist fanatics.
Indeed, it is down to the constant vigilance of the security services that Britain has not suffered another attack on the scale of the July 7 bombings in London in 2005, in which 52 people died and more than 700 were injured.