Stripping Islamic State brides like Shamima Begum of their UK citizenship would no longer be allowed under a policy approved by the Liberal Democrats.
Party members on Tuesday backed a motion taking away the Home Secretary’s unilateral right to deprive people of their citizenship.
Instead, the Secretary of State would have to apply to a UK court to have citizenship rescinded.
The move came after Sajid Javid, former home secretary and now Chancellor, decided to punish Shamima Begum for leaving her home in East London in 2015 to join IS forces, having after being radicalised in Britain, by taking her citizenship away.
He claimed Ms Begum would not be left stateless as she was eligible for Bangladeshi citizenship – despite that country’s government saying it would refuse her access.
She now resides as a refugee in Northern Syria, where her baby son died following the move to strip her of her British citizenship.
Lib Dem home affairs spokeswoman Christine Jardine criticised Mr Javid’s decision at her party’s conference in Bournemouth.
She said: “Could our national security actually have been better served by grasping the opportunity to interrogate young people – this young person who’d been recruited by Isil (another term for IS)?
“Talk to her, learn exactly how Isil does it, how they radicalise British teenagers and stop them doing it again? I think so.”
She added: “Would it really, really have been impossible to prosecute Shamima Begum in the UK? Because that’s what the home secretary argued.
“I think maybe the Conservatives need to have more faith in the British judicial system.”
Ms Jardine was speaking at the start of the party’s policy motion debate on deprivation of citizenship, which was approved by a members’ vote in the main hall of Bournemouth International Centre.
The approved motion would allow a home secretary in a Lib Dem government to apply to a court for deprivation if the citizenship was found to have been gained by fraud or the person represents a national security risk.
An amendment to abolish the ability to strip people of citizenship altogether was proposed, but not voted on.