Abu Qatada has won an appeal against deportation to Jordan where he was to face trial on terror charges, according to a ruling by the Special Immigration Appeals Court.
The decision was made despite Theresa May receiving special assurances from Jordan that evidence gained using torture would not be used against him.
The judge's provisional view is that the radical cleric could be granted bail with a 16 hour curfew.
The Home Office said it "deeply disagrees" with the ruling and will seek leave to appeal.
A Home Office spokesman said: "We have obtained assurances not just in relation to the treatment of Qatada himself, but about the quality of the legal processes that would be followed throughout his trial.
"Indeed, today's ruling found that 'the Jordanian judiciary, like their executive counterparts, are determined to ensure that the appellant will receive, and be seen to receive, a fair retrial'.
"We will therefore seek leave to appeal today's decision."
Siac found that Qatada's right to a fair trial would be breached because evidence obtained via torture could be used during his re-trial in Jordan.
Qatada had claimed that there was a risk that he himself would be tortured or badly treated in Jordan, however this was rejected.
His legal team also maintained that even if he was acquitted at re-trial, he could be kept in prison under Jordanian law if the authorities decided he was "a danger to the people", therefore breaching his right to liberty.
This was also rejected.
May is due to make a statement to the Commons on the ruling this afternoon.