A man facing terrorism charges in the US who appealed for consular assistance was told he could not receive it because the home secretary had revoked his UK citizenship.
Mahdi Hashi, who was born in Somalia, is in New York facing terrorism charges.
But when his family requested help he was told he would not receive consular assistance because he is no longer a British national.
Hashi, a former Haverstock schoolboy, grew up in Chalk Farm but now stands accused of training with an extremist group in east Africa.
He was one of 20 people stripped of their British citizenship this year because of their decision to fight in the war in Syria, it has emerged.
Latest figures from the Bureau of Investigative Journalism showed the increase was more than the total seen in the previous 30 months combined.
Those hit by the decision mean their ticket to Syria becomes effectively one-way, as in the vast majority of the cases citizenship is removed while the individual is overseas.
The move is only available in cases of dual citizenship, because international rules prevent citizenship being removed if the individual in question is left stateless.
It does not require judicial approval and is permitted under the British Nationality Act if the home secretary believes the presence of the citizen in Britain is "not conducive to the public good".
Hashi's case was appealed - the only recourse against the move in existing legislation - back in June.
Baroness Helena Kennedy QC, who unsuccessfully challenged May's decision in an immigration appeal court, told the New Journal he had been "exposed to illegality and an abuse of human rights" by the UK.
The FBI says he was "deployed in combat operations to support Al-Shabaab action in Somalia".
With between 40 and 240 Britons in Syria the likelihood is more people will see their British citizenship status revoked in 2014, it is now being predicted.
"We are probably not as quick as we should be to strip their citizenship," one former senior Foreign Office official told the Independent, which broke the story.
A Home Office spokesperson said: "Citizenship is a privilege, not a right, and the Home Secretary will remove British citizenship from individuals where she feels it is conducive to the public good to do so."