Why did it take the Americans to unmask Jihadi John? British authorities have known identity of ISIS killer for weeks – but STILL refuse to confirm his name

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The UK Government remains tight-lipped over the naming of Jihadi John (pictured, who was revealed today as Mohammed Emwazi, 26, from west London

Questions were being asked today about why it was left to the U.S. Government to reveal the identity of Jihadi John instead of British authorities.

The UK Government remains tight-lipped over the naming of the terror suspect who was revealed today as 26-year-old Mohammed Emwazi, from Queen's Park in west London.

Emwazi, who studied computer programming at the University of Westminster before travelling to the Middle East three years ago, was confirmed as the prominent ISIS figure by two U.S. Government sources.

However, while Whitehall sources confirmed Emwazi had been known to security services for several weeks, the Home Office would not release any confirmation of his identity.

Government sources said his name had not been made public because the priority was to try and locate him.

The Home Office said it was 'unable to comment' when contacted by MailOnline today, while Metropolitan Police has yet to respond to requests for comment.

Downing Street also refused to comment on Emwazi, including claims that he had contacts with MI5.

A Number 10 spokesman said: 'Our long-standing position on Jihadi John's identity is that we are neither confirming nor denying.

'There is an ongoing police investigation, we are not going to give a running commentary on that.'

Pressed on the claims Emwazi had contact with MI5, the spokesman said: 'You are asking me to speculate about speculation.

'What's right is we let the police and security services do their work in an ongoing investigation to bring these murderers to justice.'

Police could be seen attending Emwazi's home in Queen's Park earlier today, but no officers spoke to the media.

Despite official sources failing to confirm his identity, it is understood Paul Henning - the brother of British aid worker Alan who was beheaded by Jihadi John - was aware of the ISIS militant's identity.

It is also believed that he was made aware by Government officials that the name would released to the public today.

Jihadi John's identity was first published by the Washington Post, who reported that friends and family of Emwazi had confirmed he was the ISIS frontman.

The revelation was swiftly picked up by the British media, but despite being broadcast around the world, British authorities continue to remain tight-lipped. 

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The UK Government remains tight-lipped over the naming of Jihadi John, who was revealed today to be 26-year-old Mohammed Emwazi, from Queen's Park in west London. Police attended his home today (pictured)

Raffaello Pantucci, a senior research fellow at defence think tank the Royal United Services Institute, said it was no surprise that Jihadi John's outing was revealed by America.

He said: 'It will elevate him, and even add to the mythology around him in some minds.

'He has been on the radar for a long time now, and we finally know who he is.

'There is a reason the British security services would not have wanted his name to be made public, because they will have been watching his associates covertly as part of their intelligence gathering.

'The FBI said last year they knew who Jihadi John was, but my understanding is he had actually been narrowed down to one of three people, and the British and Americans were not sure which. 

'That is an example of the different attitude when it comes to revealing information.'

Jihadi John has featured in the execution videos of British aid workers Alan Henning and David Haines, U.S. journalists James Foley and Steven Sotloff, Japanese reporter Kenji Goto and Syrian soldiers.

Both UK and U.S authorities have maintained that they have been running a joint investigation to unmask the ISIS militant. 

However, while the British Government has largely remained tight-lipped about the probe, U.S. officials have been more vocal.

The U.S. Senate has also previously offered a £6million reward to anyone providing information that could lead to the capture of Jihadi John.

Last September, U.S. sources revealed that American spy planes had flown above Britain to monitor telephone and computer signals in a bid to track down the British terrorist and those communicating with him.

The aircraft, manned by British pilots and carrying FBI agents, were equipped with advanced technology to detect heat coming off a keyboard when a button was pressed.

At the time, the U.S. claimed that Jihadi John was from a suburb within 10 miles of south London, but Defence Secretary Philip Hammond said that UK officials were only 'getting warm' as to confirming his identity.

However, in the same month - perhaps reinstating the fact it was a joint investigation between the two countries - it emerged that family members of Jihadi John had been interviewed by both Met officers and an FBI agent.