Two women who were born in the UK, known only as C3 and C4, had their British citizenship removed in November 2019 on the grounds of national security.
C7, a man born in Bangladesh who became a British citizen at birth, also had his British citizenship revoked in March 2020 on the basis that he had “aligned” with Islamic State and was a threat to UK national security.
All three appealed against the removal of their British citizenship at the Special Immigration Appeals Commission (SIAC) in November.
The Home Office argued that all three were dual British-Bangladeshi nationals at the time their British citizenship was removed, and so the decision did not render them stateless.
But their lawyers said all three lost their Bangladeshi citizenship when they turned 21, meaning the decision did leave them stateless and was therefore unlawful.
In a ruling on Thursday, Mr Justice Chamberlain said: “C3, C4 and C7 have persuaded us that, on the dates when the decisions and the orders in their cases were made, they were not nationals of Bangladesh or any other state apart from the UK.
“This means that orders depriving them of their British citizenship would make them stateless.”
The judge added: “The Secretary of State had no power to make orders with that effect.
“For that reason – and that reason alone – the appeals against the decisions to make those orders succeed.”
The SIAC is a specialist tribunal which hears challenges to decisions to remove someone’s British citizenship on national security grounds.
It comes after the Supreme Court last month ruled Shamima Begum cannot return to the UK to pursue an appeal against the removal of her British citizenship.
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