Expert lawyers with experience in Bangladeshi citizenship cases have told the BBC that under Bangladesh law, a UK national like Ms Begum, if born to a Bangladeshi parent, is automatically a Bangladeshi citizen. That means that such a person would have dual nationality.
I also understand that the boy is a Dutch National by virtue of the father.
Either of these would appear to suggest that the authorities have acted within international law in banning Shamami Begum.
Perhaps Mr Corbyn and Ms Abbot have a different view and would like to offer to pick up the legal tab for Ms Begum.