The British Islamic State (Isis) militant filmed beheading Steven Sotloff is the same man who killed James Foley two weeks ago, the Foreign Secretary has confirmed.

Philip Hammond said analysis of the brutal footage of both murders has concluded it is genuine and features the same masked militant, who speaks with a distinctive London or south-east accent.

“I'm back, Obama, and I'm back because of your arrogant foreign policy toward the Islamic State [...] despite our serious warnings,” he says in the latest video.

“So just as your missiles continue to strike our people, our knife will continue to strike the necks of your people.”

He went on to threaten to kill a British hostage, who was paraded in front of cameras, next if the US and Western government did not "back off" from fighting Isis.

The terrorist has been dubbed “jihadi John” because of his reported membership of a trio of UK-born terrorists fighting with Isis in Syria nicknamed after The Beatles.

He is believed to be one of up to 500 Britons believed to have travelled to join Islamist groups in the country’s continuing civil war.

Video: Philip Hammond on IS and British hostage

The British Ambassador to the United States said last month that agencies were “not far away” from naming the militant but no identification has been made.

Speaking to CNN following the beheading of Mr Foley, an American journalist being held with Mr Sotloff, Peter Westmacott said voice-recognition and intelligence was being used to track him down.

Mr Westmacott said the problem “goes beyond one horrendous criminal.”

“People think maybe as many as 500 British subjects have gone to Syria and Iraq for this cause of jihad,” he added.

The Home Office would not comment on whether the man in the video has been identified and it is understood that, for security reasons, the knowledge would not be made public if it did exist.

A former rapper fighting with Isis in Syria is believed to be one of several British jihadists under investigation.

Abdel-Majed Abdel Bary pictured here in a YouTube video showcasing his rapping

Abdel-Majed Abdel Bary, 24, was known as L Jinny or Lyricist Jinn at home in London, where his rising music career saw him appear in videos and have his singles played on BBC Radio in 2012.

He came to national attention earlier this year, when he posted a picture of himself holding a severed head on Twitter after resurfacing in Syria.

Bary reportedly travelled to the country last year from Maida Vale, west London, where he lived with his mother and five siblings.

His father Adel Abdul Bary, an Egyptian refugee thought to be one of Osama Bin Laden’s closest lieutenants, was extradited from Britain to the United States on charges of terrorism in 2012 for his alleged roles in the bombings of two US embassies in east Africa in 1998.

Bary’s current whereabouts in Syria is not known and his Twitter account under the name “Terrorist” @ItsLJinny has been deactivated.

Previous posts mentioned Abu Hussein al Britani, a fellow Isis militant who has uploaded pictures of himself on Twitter with guns in Syria.

He and associate Abu Abdullah al-Britani were seen offering travel advice to would-be jihadists online earlier this year.

Other Britons known to have travelled to Syria include a young Scottish woman who goes by the identity Umm Layth, believed to be Glasgow-born Aqsa Mahmood, and another called Khadijah Dare.

Khadijah Dare and her husband, Abu Bakr, in a Channel 4 documentary (Channel 4)

Both travelled to Syria last year and have since married Isis fighters, posting a stream of extremist views and accounts of their new lives online.

David Cameron said the Government was doing all it could to stop people being radicalised and travelling abroad but needed stronger legal powers.

Speaking on Monday, he said existing terrorism prevention and investigation measures would be boosted and powers to revoke or refuse passports to suspected extremists would be used.

“We have also stepped up our operational response, with a fivefold increase in Syria-related arrests and the removal of 28,000 pieces of extremist material from the internet this year alone, including 46 ISIL-related videos,” he said.

In pictures: Steven Sotloff Show all 7 1 /7 In pictures: Steven Sotloff In pictures: Steven Sotloff Steven Sotloff Steven Sotloff inside Al-Fateh Mosque in Manama, Bahrain, in 2010 EPA In pictures: Steven Sotloff Steven Sotloff Journalist Steven Sotloff, left, pictured in Libya in 2011 Getty Images In pictures: Steven Sotloff Steven Sotloff Steven Sotloff pictured in 2010 near Lulu Roundabout in Manama, which later became the iconic center for the 2011 pro-reform protests in Bahrain EPA In pictures: Steven Sotloff Steven Sotloff Journalist Steven Sotloff pictured in Egypt In pictures: Steven Sotloff Steven Sotloff Media gather outside Steven Sotloff's family home in Pinecrest, Florida AP In pictures: Steven Sotloff Steven Sotloff Shirley Sotloff during a recent appeal to the captors of her son AP In pictures: Steven Sotloff Steven Sotloff Pinecrest police officers are positioned at the home of Arthur B. Sotloff and Shirley Sotloff, the parents of American freelance journalist Steven Sotloff, in Pinecrest, Florida

A spokesman for the Home Office said: “We have excluded more preachers of hate than any other UK government and the police regularly disrupt events which feature extremist preachers. Since 2010, we have taken down over 47,000 pieces of illegal terrorist material from the internet.