There are now more than twice as many British Muslims fighting for Islamic State than there are serving in the British armed forces, according to a British Member of Parliament (MP).

Khalid Mahmood, the MP for Perry Barr in Birmingham, estimates that at least 1,500 young British Muslims have been recruited by extremists fighting in Iraq and Syria in the last three years.

Mahmood told Newsweek that this figure had been building since the start of the Syrian conflict: "If you look across the whole of the country, and the various communities involved, 500 going over each year would be a conservative estimate."

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According to the Ministry of Defence, there are only around 600 British Muslims currently serving in the Armed Forces, making up approximately around 0.4% of total personnel. 4.3% of the British population are Muslim.

The UK Foreign Office said that they believe over 400 individuals have travelled to Syria since the uprising began, but said that they could not give exact numbers.

However Mahmood described such low estimates as "nonsense" and said that the British government was failing to deal with the problem of home-grown extremists. "We've not concentrated on the prevention work, we haven't invested enough in de-radicalisation. It's tragic, somebody's got to wake up to it."

The role of British jihadists fighting in the Middle East has been brought into sharp focus after Islamic State released a video showing the apparent beheading of US journalist James Foley by a masked jihadist who spoke with a British accent.

James Foley at work in Izaa district in Aleppo, Syria, Sep. 2012.

In June, three militants involved in an ISIS propaganda video were identified as Cardiff students Reyaad Khan, 20, Nasser Muthana, also 20, and his younger brother Aseel, 17.

Conservative MP Nadhim Zahawi last week told Channel 4 news that a Kurdish leader told him that Islamic State fighters in Iraq had been carrying a Liverpool FC season ticket and a gym card from Ealing in London. He estimated the number of Britons fighting for Islamic State at as many as 700.

Ghaffar Hussain of anti-radicalization charity the Quilliam Foundation argued that the number of British Muslims being drawn to Islamic State and other organisations meant that the UK was "definitely" losing the fight against radical extremism.

"There are an unacceptable number of Britons fighting for jihadist forces over the world," Hussain told Newsweek.

"There are things the government can do to prevent this of course," Hussain says. "There needs to be a greater effort in the way of civil society initiatives that discredit jihadist organisations in the UK and promote liberal democratic values."

Islamic States militants' recruitment campaign has overtaken Al-Qaeda in its effectiveness online, targeting primarily young muslims, the Quilliam Foundation told Newsweek.

"Their use of the internet is unlike anything we have seen before," Charlie Cooper of the Quilliam Foundation said.

"Social media applications like Facebook and Twitter act as a facilitator to connect young radicalized Britons with jihadists in Syria and Iraq."

Islamic State have so far run a very successful campaign of using public forums such as Twitter, Facebook and YouTube, whilst avoiding detection by authorities, with Quilliam reporting Islamic State supporters share resources on how to remain under the radar of the law.

Responding to the Islamic State video earlier today, UK-based radical Islamic preacher Anjem Choudary who is a vocal supporter of establishing a Caliphate under Islamic Sharia Law told digital radio station Fubar Radio that "it's not important if it's a British person carrying out the execution because you're Muslim first and British second".

A Home Office spokesperson told Newsweek that the British government is aware of the threat of Islamic State recruitment campaigns in the UK, insisting "the police and security services are actively working to detect and disrupt terrorist threats. People seeking to travel to engage in terrorist activity in Syria or Iraq should be in no doubt we will take the strongest possible action to protect our national security, including prosecuting those who break the law. 

"We also have a wide range of powers at our disposal to disrupt travel and manage the risk posed by returnees," the spokesperson said. 

The Ministry of Defence did not immediately respond to Newsweek's request for comment.