On Thursday, the Court of Appeal ruled Ms Begum – one of three east London schoolgirls who travelled to Syria to join the so-called Islamic State group (IS) – could only mount a “fair and effective appeal” if she was in the UK.
Mr Johnson told The Sunday Telegraph: “It seems to me to be at least odd and perverse that somebody can be entitled to legal aid when they are not only outside the country, but have had their citizenship deprived for the protection of national security.
“That, amongst other things, we will be looking at.”
The Prime Minister said that the Government would also be looking at the whole system of judicial review to establish whether it had “perverse consequences”.
“What we are looking at is whether there are some ways in which judicial review does indeed go too far or does indeed have perverse consequences that were not perhaps envisaged when the tradition of judicial review began,” he said.
Ms Begum, now 20, travelled to Syria in February 2015 and lived under IS rule for more than three years before she was found, nine months pregnant, in a Syrian refugee camp in February last year.
Then-home secretary Sajid Javid revoked her British citizenship on national security grounds later that month.
Ms Begum took legal action against the Home Office, claiming the decision was unlawful because it rendered her stateless and exposed her to a real risk of death or inhuman and degrading treatment.
The Home Office spokeswoman said it would be applying for permission to appeal against the court’s judgment.