Shamima Begum is one of more than 150 people subjected to the measure for the “public good” since 2010.
The removal of citizenship means the 19-year-old has no right to enter the UK or gain a British passport, and cannot request assistance to leave the Syrian camp where she is currently detained with her newborn son, Independent reported.
Ms Begum’s family are to launch a legal challenge, and their lawyer said the teenager, who could have automatic Bangladeshi citizenship through her mother, was born in the UK and had never been to Bangladesh or possessed a Bangladeshi passport.
Official statistics show citizenship deprivations were used only a handful of times a year, until they rocketed from 14 people in 2016 to 104 in 2017.
The Home Office declined to give a reason for the dramatic increase, and said it could not provide a breakdown of how many Isis members were involved or the justification for each case.
The government has argued that citizenship deprivations protect the public, but critics accused it of abdicating responsibility and setting a “dangerous precedent”.
The British Nationality Act 1981 gave home secretaries the power to deprive people of British citizenship if their presence was “not conducive to the public good” or if their nationality was gained fraudulently.
But in 2014 the government extended the law to let the power be used even when people would be made stateless, if they have “conducted themselves in a manner seriously prejudicial to the vital interests of the UK”.
“In practice, this power means the secretary of state may deprive and leave a person stateless if that person is able to acquire (or reacquire) the citizenship of another country,” official guidance states.
Hailing the change in November 2014, the then home secretary Theresa May said the power had been used because of terrorist activity in the “overwhelming majority” of cases.
However, the revoking of British citizenship in the case of Shamima Begum has been widely criticised.
Diane Abbott MP, Labour’s shadow home secretary, said “fundamental freedoms do not need to be compromised” for public safety.
“If the government is proposing to make Shamima Begum stateless, it is not just a breach of international human rights law but is a failure to meet our security obligations to the international community,” she said.
Conservative former minister George Freeman criticised the move as a “mistake” that will set a “dangerous precedent”.