The jihadi twin caught trying to enter Syria had already had a seven-month stay there with her toddler son, it emerged yesterday.
Jamila Henry, 21, lived with two-year-old Mustafa in the Islamic State stronghold of Raqqa until just before Christmas.
She came back to Britain to leave him with family before trying to return to Syria. On Monday Turkish police picked her up in the capital Ankara.
Henry managed to flee the UK for a second time despite being on the radar of MI5, whose agents tried to recruit her.
Wedding day: Jamila Henry with her estranged husband, whose identity is being protected
They interviewed her, gave her a smartphone and repeatedly contacted her. But, under their noses, she was able to steal her glamorous identical twin’s passport and head back to the conflict zone.
The astonishing lapse comes weeks after it emerged that Mohammed Emwazi – the Islamic State butcher called Jihadi John – was known to the security services for five years and they had tried to recruit him too.
Despite being classed as a priority target, Emwazi managed to travel to the Middle East and start his reign of terror in Syria. Michael Adebolajo, one of the killers of Lee Rigby in Woolwich, was also courted by MI5.
Last night, a friend of the Henry family lashed out at ‘bumbling’ MI5 officers, accusing them of trying to cover up their mistakes.
‘They are a joke,’ said the source. ‘They keep calling everyone to find out what happened and telling them what they should and shouldn’t say to people.
Travel: Ms Henry tried to use a passport, left, which belonged to her ‘party girl’ twin sister Jalila, right
‘They were all over the family for months after Jamila came back but were left whistling in the wind when she disappeared again.’
Under surveillance: Jamila Henry was questioned by MI5 before she fled to try and travel to Syria
Henry returned in December under pressure from relatives including her estranged husband. A source close to the family said: ‘Her husband had no idea she was going to take Mustafa to Syria. He was extremely glad when they both returned safely.
‘He and his parents were distraught and traumatised in the months the baby was missing.
‘He in particular struggled not knowing where his son was or whether or not he was safe. It was a testing time.
‘He suffered many sleepless nights fearing he would never see his child again. He had no contact with Jamila. All he could do was send messages via her family pleading for her to return his son and just prayed that his pleas would reach her.’
Henry was stopped and questioned for up to nine hours by MI5 officers and detectives from Scotland Yard’s counter-terrorism command when she returned home with Mustafa in December.
They released her without her being arrested or charged in the belief that she would co-operate with them as they investigated her movements and contacts in Syria.
Henry converted to Islam in her teens and moved to east London where she had an arranged marriage with her husband, a Muslim Turkish Cypriot. The couple soon had their child but their relationship collapsed when Henry began spouting radical beliefs.
Her latest journey to Turkey was on the passport of her ‘south London party girl’ twin sister Jalila.
Yesterday Henry remained under arrest at a high-security central London police station after being flown back from Turkey to Luton airport on Thursday. She is being held on suspicion of preparing acts of terrorism, an offence which carries a maximum penalty of life imprisonment.
She is the latest woman to flee the UK to join the barbaric terrorist group as a jihadi bride and support its frontline fighters.
Last month three ‘straight A’ east London schoolgirls, aged 15 and 16, abandoned their families to travel to Syria via Turkey.
They were following in the footsteps of a friend who joined Islamic State in December. All four went to the same Bethnal Green school.
Jihad: Ms Henry is thought to have been heading to ISIS-controlled territory; pictured is their capital Raqqa