Questions have been raised over the role of border officials in preventing aspiring jihadis travelling to Syria.

Intelligence agencies and the police are responsible for detaining suspected extremists at the border, while limits on the ages of passengers are set at the discretion of airlines.

But following the disappearance of 15-year-old Briton Yusra Hussien, who is understood to have flown to Istanbul from Heathrow in a bid to reach Syria – a now well-established route taken by potential foreign fighters to Syria – in the UK questions over whether more can be done have been raised.

The border should be made stronger and exit checks should be the norm

David Hanson, shadow immigration minister, said: “The key is to stop radicalisation in the first place and that’s why Labour’s ‘Prevent’ programme, cut by this Government, was so vital.

“There are questions to be asked about whether the Border Force should have intervened on seeing a single minor travel unaccompanied and whether more checks should be undertaken.

“The border should be made stronger and exit checks should be the norm.

“More widely we need to be working much more closely with our allies in Europe to ensure that young British citizens who may have left the UK cannot make it into the clutches of brutal groups like Islamic State.

“In particular, we need to be working alongside Turkish border forces to support them to identify those who may be travelling from Turkey into Syria or Iraq.”

Two airlines fly to Turkey from Heathrow – British Airways and Turkish Airlines.

On Wednesday, a family friend of the Hussiens, Labour councillor Afzal Shah, said it was unclear whether or how the teenager had purchased a plane ticket.

“That's something the family and police are trying to establish,” Mr Shah said. “But this also begs the question, how could a 15-year-old child be allowed to board a plane, just like that?”