Home Secretary Sajid Javid stripped Isis bride Shamima Begum of UK citizenship last week but he has now indicated that it may be prove difficult to enforce.
Speaking at the home affairs committee, Mr Javid admitted that the power can not be used if it leaves an individual stateless.
While not commenting specifically on Begum’s case, Mr Javid said: “If an individual only has one citizenship, then generally the power cannot be used because by definition if you took away their British citizenship they would be stateless.
“I certainly haven’t done that and I am not aware that one of my predecessors has done that in a case where they know an individual only has one citizenship, as that would be breaking international law as we understand it.”
It had been thought that Begum, who travelled to Syria from London to join Isis when she was 15, travelled to the UK on a Bangladeshi passport when she was a toddler, meaning she would not be made stateless.
However, Bangladesh officials have denied she has citizenship there and Begum remains in a refugee camp with her newborn baby.
Asked about a 2014 amendment to the Nationality Act that allows UK citizenship to be removed if there are “reasonable grounds for believing” the person would be able to become a citizen of another country, Mr Javid added: “I have not deployed the power on the basis that someone could have citizenship to a second country.
“I’ve always applied it on the strict advice of legal advisers in the Home Office and more broadly in the Government that when the power is deployed, with respect to that individual, they already have more than one citizenship.”
If Begum does not have Bangladeshi nationality, it would appear that the UK would not be able to strip her of citizenship.
Mr Javid hit back at suggestions his decision to revoke Begum’s citizenship was politically motivated.
He said: “This power has been used by successive home secretaries and governments of different political persuasions.
“These decisions are never political in any way. It’s all about the job the Home Secretary has to protect the British public.
“This is not some sort of new national security tool that I just invented or just rolled out. It goes back over 100 years.”
The British Nationality Act 1981 provides the Home Secretary with the power to strip someone of their citizenship if they are satisfied such action is “conducive to the public good”.
Mr Javid acknowledged that it “might be a blunt tool”, adding: “It should only be used in the most exceptional circumstances and cannot be used lightly.”