One of the UK's former leading chiefs on counter-terrorism has said would-be jihadis should be allowed to surrender their British passports and travel to join extremist groups.

Robert Quick, the former assistant commissioner at Scotland Yard said Britons who wish to go to Isis-controlled areas in Iraq and Syria should be allowed to.

"If they want to go, you have to ask the question, are we better off, if they surrender their passports and go? It’s better than them festering away here", the former head of special operations from 2008-09 told the Guardian.

Police take part in a counter-terror exercise drill in central London on 30 June (Ben Stansall/AFP)

"Should we say we’ll lay on charter flights to Syria; turn up with your passport and if you are over 18, if this is the life you want, then go?", Mr Quick asked.

Any members of the public wishing to join extremist groups abroad would forfeit their passports and never be allowed to return to Britain, he said.

Currently counter-terror forces are working to stop British people from defecting to Isis territories although as many as 1,000 people are estimated to have done so.

Ten years on today from the 2005 terrorist attacks in London, which saw 52 people murdered in four separate bombings, Britain is at an even higher terror threat level.

The national terror threat level is now standing at "severe", meaning an attack is "highly likely", according to experts at the Royal United Services Institute (RUSI).

In pictures: The 10th anniversary of the 7/7 London bombings Show all 26 1 /26 In pictures: The 10th anniversary of the 7/7 London bombings In pictures: The 10th anniversary of the 7/7 London bombings 7/7 bombings anniversary Security staff and workers from Hyde Park observe a minutes silence at the 7/7 memorial in Hyde Park In pictures: The 10th anniversary of the 7/7 London bombings 7/7 bombings anniversary People pause for a minutes silence at Kings Cross Underground station in London, as Britain remembers the July 7 attacks amid a welter of warnings about the enduring and changing threat from terrorism a decade on In pictures: The 10th anniversary of the 7/7 London bombings 7/7 bombings anniversary Members of staff working within the grounds observe a minutes silence to commemorate the tenth anniversary of the July 7 terrorist attacks at the All England Lawn Tennis and Croquet Club, Wimbledon In pictures: The 10th anniversary of the 7/7 London bombings 7/7 bombings anniversary Police officers within the grounds observe a minutes silence to commemorate the tenth anniversary of the July 7 terrorist attacks at the All England Lawn Tennis and Croquet Club, Wimbledon In pictures: The 10th anniversary of the 7/7 London bombings 7/7 bombings anniversary Representatives from 7 Company, Coldstream Guards and HQ London District join the national act of remembrance for the 7th July bombings 10th year anniversary beside the Ministry of Defence Main Building in central London and led by Rabbi Major Reuben Livingstone In pictures: The 10th anniversary of the 7/7 London bombings 7/7 bombings anniversary People observe a nationwide minute's silence on the 10 year anniversary of the 7/7 London attacks which killed 52 people, facing in the direction of a plaque and flowers laid at the location of where a suicide bomber blew themselves up during the morning rush hour on a bus in Tavistock Square In pictures: The 10th anniversary of the 7/7 London bombings 7/7 bombings anniversary George Psaradakis (centre), the driver of the number 30 bus which was blown up in Tavistock Square, looks at floral tributes left close to the scene of the bombings in London In pictures: The 10th anniversary of the 7/7 London bombings 7/7 bombings anniversary People stop to observe a minute's silence at Aldgate underground station, in memory of the victims of the July 7 bombings In pictures: The 10th anniversary of the 7/7 London bombings 7/7 bombings anniversary Flowers left by the July 7 memorial plaque at Aldgate Station, London, which names those who were killed in the bombings at the station In pictures: The 10th anniversary of the 7/7 London bombings 7/7 bombings anniversary Members of various religious groups pray during a service in St Paul's Cathedral, to commemorate the tenth anniversary of the London Bombings in London In pictures: The 10th anniversary of the 7/7 London bombings 7/7 bombings anniversary Poppy petals fall from the roof during a service in St Paul's Cathedral, to commemorate the tenth anniversary of the London Bombings in London PA In pictures: The 10th anniversary of the 7/7 London bombings 7/7 bombings anniversary A police officer looks at flowers left at Kings Cross Underground station in London In pictures: The 10th anniversary of the 7/7 London bombings 7/7 bombings anniversary Flowers left by the July 7 memorial plaque at Aldgate Station In pictures: The 10th anniversary of the 7/7 London bombings 7/7 bombings anniversary Boris Johnson and David Cameron place wreathes at the July 7 memorial in Hyde Park, London In pictures: The 10th anniversary of the 7/7 London bombings 7/7 bombings anniversary David Cameron and Boris Johnson take part in a wreath laying ceremony in London's Hyde Park, in memory of the 52 victims of the 7/7 London attacks In pictures: The 10th anniversary of the 7/7 London bombings 7/7 bombings anniversary David Cameron and Boris Johnson during a ceremony at the memorial to the victims of the July 7, 2005 London bombings, in Hyde Park In pictures: The 10th anniversary of the 7/7 London bombings 7/7 bombings anniversary From left: Paul Crowther, Chief Constable, British Transport Police, Adrian Leppard, Commissioner City of London Police, and Sir Bernard Hogan-Howe, Commissioner of the Metropolitan Police, carry wreathes at the July 7 memorial in Hyde Park In pictures: The 10th anniversary of the 7/7 London bombings 7/7 bombings anniversary People look at flowers left in Tavistock Square In pictures: The 10th anniversary of the 7/7 London bombings 7/7 bombings anniversary 7/7 survivor Gill Hicks (centre) arrives with flowers at Russell Square tube station In pictures: The 10th anniversary of the 7/7 London bombings 7/7 bombings anniversary People embrace outside Edgware Road tube station, as Britain remembers the July 7 attacks In pictures: The 10th anniversary of the 7/7 London bombings 7/7 bombings anniversary A lady carrying flowers leaves Russell Square tube station In pictures: The 10th anniversary of the 7/7 London bombings 7/7 bombings anniversary Faith leaders promote religious unity in central London, as Britain prepares to mark 10th anniversary of the 7/7 London bombings in which 52 people were killed In pictures: The 10th anniversary of the 7/7 London bombings 7/7 bombings anniversary Gill Hicks, (L) a survivor of the 7/7 London terror attacks, embraces police constable Andrew Maxwell outside Kings Cross Station in London, during an event to launch a walk by faith leaders promoting religious unity ahead of the anniversary of the attacks In pictures: The 10th anniversary of the 7/7 London bombings 7/7 bombings anniversary A memorial dedicated to the 52 people that were killed during the 7/7 terror attacks in London is pictured in London's Hyde Park In pictures: The 10th anniversary of the 7/7 London bombings 7/7 bombings anniversary The July 7 memorial in Hyde Park In pictures: The 10th anniversary of the 7/7 London bombings 7/7 bombings anniversary A memorial dedicated to the 52 people that were killed during the 7/7 terror attacks in London is cleaned in London's Hyde Park

Margaret Gilmore, a senior associate fellow specialising in national security at RUSI and a former BBC home affairs correspondent at the time of the attack, told The Independent that the threat is greater because it is now "more diverse".

"Isis has emerged as an organised, powerful and barbaric group which has developed the ability to lure support among extremists from across the globe."

Following the terror attacks on British tourists in Tunisia, last week, British security forces held two days of large-scale training exercises in London, around the disused Aldwych tube station, focussing on what might happen if a lone gunman or bomber targeted the UK.

Andrew Parker, the director general of MI5, said in a statement marking the 7/7 anniversary: "We had always known - and said publicly - we simply can’t find and stop every terrorist plot. We could not have prevented 7/7."