New anti-terror laws are being considered by home secretary Theresa May to prevent airlines from carrying suspect passengers on routes known to be used by aspiring jihadists.

Terror suspects and “children” who may be attempting to leave the UK to become involved in “terrorism-related activity” would be prevented from boarding aircraft, under legislation due to go before parliament this week.

Airlines would have to produce their passenger lists and seek “authority to carry” on certain routes known to be used by Britons trying to reach Isis-controlled territory.

High-risk passengers would be flagged up under an automatic system and blocked from boarding.

The government is also preparing to introduce a £50,000 fine for airlines that refuse to hand over passenger lists of people flying to the UK. One in five airlines currently refuses to provide these lists, the Sunday Times reported.

The move comes as it emerged that three teenage girls from London who secretly left the UK are believed to have reached Raqqa, the Syrian stronghold of Isis, also known as Islamic State.