Security services and intelligence agencies have been braced for an attack in the form of the Paris outrage since terrorists wreaked havoc in Mumbai seven years ago.
The killing of 165 people in the Indian city in November 2008 brought a new dimension to the war on terror with the emergence of the threat of a roaming, mass casualty attack.
Gunmen launched attacks at luxury hotels and major landmarks, triggering three days of fierce fighting with security forces over three days.
Since then, counter-terrorism units in the UK have been preparing for a strike involving marauding gunmen and multiple suicide bombers.
In the wake of Friday’s events in the French capital, David Cameron made clear that the threat against the UK remains.
He said: “Ever since the co-ordinated firearms attacks in Mumbai in 2008, we have all been working together to ensure we could respond to such an attack.
“It is clear that the threat from Isil is evolving.
“Last night’s attack suggests a new degree of planning and co-ordination and a greater ambition for mass casualty attacks.
“And we must recognise that however strong we are, however much we prepare, we in the UK face the same threat. That’s why we continue to encourage the public to remain vigilant.”
Earlier this year police tested their response to such an incident by carrying out a simulated attack.
The mock exercise in London saw officers and emergency services respond to reports of shots fired by a group of men who disappeared into the underground network.
There have also been reports that Scotland Yard has assembled an SAS-style unit of armed officers to counter the threat of a terrorist gun attack.
Mr Cameron confirmed that the current threat level will remain at severe, which indicates that an attack is seen as highly likely.
The outrage in Paris comes in a year which has seen France gripped by the threat of terrorism.
The developments brought back memories of January, when one of the world’s great cities was brought to a standstill by Islamist extremists.
On that occasion the French capital was rocked first by the Charlie Hebdo atrocity, when 12 people were killed after gunmen stormed the offices of the satirical magazine.
The sense of panic heightened when there was a subsequent attack on a kosher supermarket, and the incidents triggered worldwide outrage.
Since then there have been a number of more minor strikes or attempts.
In one, three Americans and a Briton overpowered a heavily armed gunman on a train from Amsterdam to Paris.
The horrific scenes in the city on Friday night represent an escalation compared with the previous incidents. It is the deadliest atrocity on French soil in recent times – in 1961 a train bombing killed 28 people.