In a ruling in February, Mr Justice Jay said that while there was a “credible suspicion that Ms Begum was recruited, transferred and then harboured for the purpose of sexual exploitation”, this did not prevent then-home secretary Sajid Javid from removing her citizenship.
Following the decision, Ms Begum’s lawyers said they would be challenging the ruling and that the legal battle was “nowhere near over”.
A three-day hearing at the Court of Appeal in London is expected to begin on Tuesday.
During the five-day hearing in November 2022, Ms Begum’s lawyers argued she should have been viewed as a victim of child trafficking and that she was “persuaded, influenced and affected with her friends by a determined and effective Isis propaganda machine”.
This Secretary of State… maintains that national security is a weighty factor and that it would take a very strong countervailing case to outweigh it— Mr Justice Jay
In the ruling, Mr Justice Jay said the case had been “of great concern and difficulty”.
He continued: “This Secretary of State... maintains that national security is a weighty factor and that it would take a very strong countervailing case to outweigh it.
“Reasonable people will profoundly disagree with the Secretary of State, but that raises wider societal and political questions which it is not the role of this commission to address.”
The hearing before the Lady Chief Justice Lady Carr, Lord Justice Bean and Lady Justice Whipple is due to begin at 10.30am.