Is Shamima Begum entitled to Bangladeshi citizenship?
By Clive Coleman, BBC legal correspondent
Lawyers have told the BBC that under Bangladesh law, a UK national born to a Bangladeshi parent is automatically a Bangladeshi citizen - a dual national - but the Bangladeshi authorities assert that's not the case for Ms Begum.
Under this "blood line" law, Bangladeshi nationality and citizenship lapse when a person reaches the age of 21, unless they make active efforts to retain it.
So, it is Ms Begum's age, 19, that is likely - in part - to have given Home Office lawyers and the home secretary reassurance there was a legal basis for stripping her of her UK citizenship.
In 2017, the government lost an appeal case brought by two British citizens of Bangladeshi origin who were stripped of their citizenship when they were abroad.
The Special Immigration Appeals Commission ruled that E3 and N3 had not tried to retain their citizenship before they reached the age of 21, and so it had automatically lapsed.
That meant that the decision to strip them of their UK citizenship had rendered them stateless.
Ms Begum's case is different. Her Bangladeshi citizenship, if established, would remain intact until she reaches 21, even if she has never visited the country or made active efforts to retain her citizenship.