Woolwich killing: the random attack has always been MI5's greatest fear
The Woolwich attack has all the hallmarks of the very nightmare MI5 has feared – low key fanatics arming themselves with basic weapons and targeting a soldier or other victim at random.
The police and security services have had repeated success since the 7/7 outrage in 2005, which left 52 innocent people dead, but they have been under constant threat of the lone wolf terrorist.
Dubbed the “Nike terrorists” after the sports giant’s slogan “Just Do It”, Britain has faced a new generation of Islamic extremists that are virtually impossible to detect.
They are self-starting fanatics who have radicalised themselves over the internet and while many may be inspired by al-Qaeda they do not need any command or control from the terror group.
MI5 was last night urgently investigating the alleged assailants in the Woolwich attack and trawling their systems to see if they were known to them or had ever crossed their radar.
But the nature of the new threat is often such attacks can come out of nowhere, with no network or obvious plot for MI5 or the police to pick up on in advance.
In 2010, Roshonara Choudhry was convicted of attempting to murder the MP Stephen Timms with a knife at his constituency office having radicalised herself.
Earlier this year a group of Birmingham terrorists only narrowly missed attacking a rally by the English Defence League through their own incompetence.
The security services only picked up on the group after they had turned up late for their target and were stopped by a traffic officer driving home in a car without insurance.
The group had knives, guns and viable homemade bombs the last of which they had built from terror material on the internet.
Senior Whitehall sources have regularly expressed relief that random, basic but deadly attacks have not been more common place in the UK.
The threat of self starters increased dramatically with the emergence of the Yemen-based al-Qaeda preacher Anwar al – Awlaki.
He gave sermons in English over the internet and encouraged followers anywhere to launch whatever attack they could, spawning the "Just Do It" motto.
Awlaki was killed in 2010 but his influence has long resonated and almost every fanatic convicted of terror plots in the UK in recent years have been inspired by him.
Last year, the then Director General of MI5, Jonathan Evans warned that one of the biggest threats to the UK was from “lone actors”.
John O’Connor, a former Flying Squad commander at Scotland Yard, said: “This has all the hallmarks of a very low key terrorist incident which raises a number of problems for the authorities.
“This type of attack is very difficult to protect against because it is not as though you are talking about a network of people following their plans.
“This raises the whole ball game.
"The bottom line of it is that this could spring up anywhere and that's the concern. It's very difficult to keep a tab on where this is going and where the threat level is."
He added: “It seems to me that this is a departure from the established type of attacks that you see or the established plans that you see of terrorism causing mass murder.
"You're into a new round of terror threats in this country, particularly as you don't know the full extent of it.
"As you don't know that – and I don't suppose the authorities know that – they have got to look at the worst case scenario.
"It is pretty horrific what has happened to this poor fella – to be murdered outside his own barracks just because he's a soldier, or at least that's what it looks like to me."
The security services and police have foiled more than a dozen terror plots on UK soil since 2005, including a major plot in every year since then.
They have included a plot to blow up airliners with liquid based bombs in 2006, targeting shopping centres and nightclubs with fertiliser based explosives, plans to target the Stock Exchange and this year 11 men were jailed as part of a plot to attack the UK with eight suicide bombers.
But the threat to soldiers has also been constant.
In 2008, a Muslim terror group was jailed for planning to kidnap a solder and film his execution.
And earlier this year three men were jailed for a terror plot that included targeting the military-linked town of Wootton Bassett.