The justices voted 6-3 not to review the case of Jose Padilla, one of the most high-profile cases testing the administration’s anti-terrorism powers in the wake of the 9/11 attacks. Mr Padilla, a US citizen captured in Chicago, was held in military detention without charges for three years before the government decided to try him in the civilian court system.

The shift to try Mr Padilla as a civilian was widely criticised as an attempt by the administration to avoid a Supreme Court review of the case, and the tactic appears to have worked.

Three justices who held the balance of power in the case – Chief Justice John Roberts, Justice Anthony Kennedy and Justice John Paul Stevens – took the unusual step of issuing an opinion to justify their refusal to hear the case, focusing on the fact that Mr Padilla is no longer being held as an enemy combatant.

“Any consideration of what rights he might be able to assert if he were returned to military custody would be hypothetical, and to no effect, at this stage of the proceedings,” Justice Kennedy wrote for the three men, noting that civilian custody was “part of the relief he sought, and that its lawfulness is uncontested”.

Justice Kennedy acknowledged that Mr Padilla “has a continuing concern” that he might be reclassified as an enemy combatant but said that concern “can be addressed if the necessity arises”. But he also issued a veiled warning to the government not to return Mr Padilla to the military, and invited him to bring his appeal straight back to the Supreme Court if they did so. At the moment, no US citizens are being held as enemy combatants.