Hundreds of British jihadis returning from fight in Syria spark terror alert after police and MI5 thwart Mumbai-style attack on London

250 British based 'extremist tourists' have returned home from fighting

Figure includes several 'veterans' who fought in Afghanistan and Pakistan

Security forces thwarted 'serious plot' by jihadis returning last Autumn

Hundreds of British jihadis have returned from fighting in Syria, sparking a terror alert in Britain.



Senior security officials have said that around 250 British based 'extremist tourists' have returned home, and are now suspected of wanting to carry out attacks here.



The figure is five times higher than previously thought and includes several 'veterans' who have fought in Afghanistan and Pakistan.



Fighting: Security officials are closely monitoring 250 British-based jihadis linked to the Syria. Above, rebel fighters fire a rocket-propelled grenade at an army checkpoint in the Ain Tarma neighborhood of Damascus

MI5 and police have already intercepted an alleged serious plot by jihadis returning from the war torn region last Autumn.



They were said to be planning a Mumbai-style gun attack on civilians in a crowded place, possibly London.



The returnees are now being monitored by the security services, The Sunday Times reports.

A senior Whitehall security official told paper: 'Well over half of those who travelled out have come back.'

Last week it was announced that extremist videos which help to radicalise impressionable young men are to be blocked from the internet in the UK.

The Home Office is in talks with web companies to refuse access to violent films hosted overseas 'at a network level', MailOnline can reveal.



The plans for what will effectively be ‘cyber border controls’ have been drawn up by James Brokenshire, promoted to immigration minister at the weekend.

Conflict: Around 400 extremists are believed to have travelled to Syria. Above, a rebel clutches his head

Ministers were spurred into action by the growing threat from jihadists in Syria.

Around 2,000 Europeans are thought to be fighting in Syria, including at least 200 known to the British security services.

It is feared that fighters returning to the UK will seek to radicalise young men in particular to launch terror attacks at home and abroad.

Anti-terror police and the Crown Prosecution Service can currently demand that vile videos posted on UK websites be removed.

Since February 2010, the Counter Terrorism Internet Referral Unit (CTIRU) has taken down more than 21,000 pieces of illegal terrorist online content.

If the CTIRU and prosecutors deem material to be illegal it can be blocked from parts of the public sector, including schools and hospitals but this does not extend to domestic users and filters can be turned off.

Last week, v ideo footage capturing the final moments of a British suicide bomber's life was released by a terrorist group in Syria.

The clip, recorded by the al-Qaeda-aligned group Jabhat al-Nusra , shows Abdul Waheed Majeed relaxing and smiling moments before he carried out the suicide attack, the first by a Briton.

In the 'martydom' video, the 41-year-old is seen wearing white Muslim robe while posing for photos with fellow soldiers and pointing up to the sky.

Married father of three Majeed is suspected of driving a lorry into a jail in Aleppo and detonating a bomb last week.

Officials have not confirmed the identity of the bomber amid reports that a UK jihadi, who used the name Abu Suleiman al-Britani, carried out the bombing.

Counter-terrorism officers have searched Majeed’s home in Crawley which is also the ex-home of schoolgirl Sarah Payne’s killer Roy Whiting, according to neighbours.

Majeed, known as Waheed, left Britain six months ago, telling his family he was going on a humanitarian mission to Syria.