Sir Ed Davey has urged the home secretary to "step up to the plate" and bring Shamima Begum back to the UK.
In an interview on the Matthew Wright show, the Liberal Democrat spokesman said the the IS teen was a "British citizen" and therefore a "British responsibility".
"Whose responsibility does the home secretary think this woman is?" Sir Ed told Wright, and co-host Kevin.
- Read more: Begum family plead with Sajid Javid to help bring IS teen's baby to Britain
- Read more: Shamima Begum: 288,100 votes cast in talkRADIO poll
"The law is clear that if she doesn't have another citizenship, she can't be made stateless."
The MP for Kingston and Surbiton added that Javid was avoiding his "responsibilities" by leaving the Jihadi bride in a Syrian refugee camp.
'Step up to the plate'
Home secretary Sajid Javid. Image: Getty
"If you're going to take on problems like this and deal with terrorist threats and people who encourage and support terrorism, then you shouldn't just hand it over to someone else," he said.
"You should step up to the plate and take on your responsibilities, and the home secretary is failing to do that."
He added: "I want to know how to improve national security. Here you have a huge opportunity to interview these people, to really grill them."