The 25 lines edited out of the court papers contained details of how Mr Mohamed's genitals were sliced with a scalpel and other torture methods so extreme that waterboarding, the controversial technique of simulated drowning, "is very far down the list of things they did," the official said.

Another source familiar with the case said: "British intelligence officers knew about the torture and didn't do anything about it. They supplied information to the Americans and the Moroccans. They supplied questions, they supplied photographs. There is evidence of all of that."

David Davis, the former shadow home secretary who first highlighted the case, said: "What has become clear is that the information being held back is not protecting the American government who have made a clean breast of their involvement in torture, but the British government, where at least two cabinet ministers have denied any complicity whatsoever.