A 52-year-old British man who described himself as a teacher when he hired a car he would later use to murder two people was responsible for the terror attack on Westminster, according to police.

Scotland Yard said they believed that Khalid Masood, thought to be a father-of-three, was the man who killed three including a police officer, during a murderous rampage before he was himself shot dead.

He had a string of convictions for assaults, including GBH, possession of offensive weapons, including knives, and public order offences.

Although never convicted of terror offences, Theresa May was forced to admit that he had been investigated by MI5 over links to extremists.

But, the Prime Minister told MPs, he had been regarded as a "peripheral figure" who was not "part of the current intelligence picture".

Within hours Amber Rudd, the Home Secretary, defended the security services saying that no "finger of blame" could be pointed at them.

At the same time the Islamic State terror group described Masood as a “soldier” who had answered their call to attack.

But experts accused IS of a pattern of making opportunistic claims about international terror incidents.

Last night three women and five men were also arrested on suspicion of preparing terrorist acts, following raids in London and Birmingham.

Masood, who was also known by a number of aliases, was born in Kent on Christmas Day, 1964.

He is reported to have been a Muslim convert and former English teacher who was obsessed with body-building.

Detectives believe he had been recently living in the West Midlands, the location of much of the focus of the investigation.

Scotland Yard said that Masood had not been the subject of any live inquiries before Wednesday's attack and there had been "no prior intelligence about his intent to mount a terrorist attack".

A huge police operation across the UK, involving hundreds of officers, is trying to piece together what happened and if Masood had links with IS.

But investigators are currently working on the theory that he acted alone.

Before he was named Mrs May told MPs that police believed that the terrorist was British-born and had once been investigated in relation to concerns about violent extremism some years ago, but had been considered a "peripheral figure".

Later Ms Rudd defended the security and intelligence agencies.

She said that it would be "wrong" to assume an intelligence failure.

"I think we have to be careful before we point any finger of blame at the intelligence services. They do a fantastic job,” she said. “The fact that he was known to them doesn't mean that somebody has 24-hour cover.”

She also cast doubt on the claim by IS, also known as Daesh, that Masood was a "soldier".

"We all know Daesh, we all know that they want to have a terrorist attack in the UK," she said.

She said it was unclear if the claim was true but that “what we do know is that they want to exploit (the attack) by putting fear into people and saying it was all about them. We will see."

She added that she did not think the government needed new powers or extra resources to fight terror.

"I think that the Government and the country has the tools that it needs to combat terrorism," she said.

“I don't think it would be right now to have some knee-jerk reaction and introduce something new."

But there could be "lessons to learn", she added.

In its first public pronouncement since the atrocity, IS said in a statement: "The attacker yesterday in front of the British Parliament in London was a soldier of the Islamic State executing the operation in response to calls to target citizens of coalition nations."

However, experts warned that the terror organisation has a record of claiming attacks.

They also said it was significant that the IS statement did not appear to claim that the group itself had directed the strike, but was merely suggesting that Masood had been 'inspired' by its call to action.

Governments across the world fear that the number of IS-related terror attacks could rise as the group is increasingly pushed out of its strongholds in countries like Iraq and former fighters are forced to return to their home nations.