The head of MI6, the Secret Intelligence Service, has insisted it has "nothing whatsoever" to do with torture but warned that it had to work with agencies from other countries which were not always "friendly democracies".
In the first public speech by a serving MI6 chief, Sir John Sawers warned that innocent lives could be lost if his service did not pass on intelligence drawn from suspects who might have been treated badly.
Sawers said MI6 had a duty to try to ensure its partners around the world respected human rights. But he said it presented a constant dilemma because it was also his duty to protect Britain.
"Suppose we received credible intelligence that might save lives, here or abroad. We have a professional and moral duty to act on it. We will normally want to share it with those who can save those lives," he said.
"We also have a duty to do what we can to ensure that a partner service will respect human rights. That is not always straightforward. Yet if we hold back, and don't pass that intelligence, out of concern that a suspect terrorist may be badly treated, innocent lives may be lost that we could have saved.
"These are not abstract questions just for philosophy courses or searching editorials, they are real, constant operational dilemmas."
Sawers said ministers had to take responsibility for the more controversial decisions. "Sometimes there is no clear way forward. The more finely balanced judgments have to be made by ministers themselves."
He went on: "If we know or believe action by us will lead to torture taking place, we're required by UK and international law to avoid that action. And we do, even though that allows the terrorist activity to go ahead.
"Some may question this, but we are clear that it's the right thing to do. It makes us strive all the harder to find different ways, consistent with human rights, to get the outcome that we want."
Sawers said that if MI6 was to succeed in countering the threat, it was essential that its agents and other intelligence agencies could be sure their secrets were protected.
"Secrecy is not a dirty word. Secrecy is not there as a cover-up. Secrecy plays a crucial part in keeping Britain safe and secure," he said.