London ? Britain’s top spy came in from the cold of a crisp autumn morning Thursday to condemn torture, warn of nuclear proliferation and defend the shadowy world of covert intelligence-gathering as crucial to keeping the country “safe and secure.”

John Sawers, the chief of the Secret Intelligence Service, made the comments in an unprecedented public speech in which he tackled allegations of British complicity in the abuse of terror suspects and pleaded with his compatriots to understand that, despite an ever-increasing trend toward official transparency, “secrecy is not a dirty word.”

While it may have seemed odd for the leader of such a cloak-and-dagger organization to go on live national television to make the case for secrecy, Sawers is no ordinary spy: He is undoubtedly the first intelligence chief to have had his photo splashed on his wife’s Facebook page showing him frolicking on the beach.

His message to an audience of journalists and academics was a serious one, however. Sawers said his agency, also known as MI6, helped keep Britain safe through a network of dedicated but unsung agents, some posted in far-off and dangerous lands, who provided the government with important information.

“We get inside terrorist organizations to see where the next threats are coming from,” he said. “What we do is not seen.”

Sawers said integrity remained the intelligence service’s most prized value, and he insisted that his agents were committed to “basic decency and moral principles” in spite of accusations that Britain has turned a blind eye to abusive practices by other countries’ spies and accepted intelligence from them.

“Torture is illegal and abhorrent under any circumstances, and we have nothing whatsoever to do with it,” Sawers declared.

But he acknowledged that his work often presented difficult ethical conundrums. What if, for example, Britain came upon credible evidence of a terrorist plot in another country but knew that turning over such information to the country involved could result in suspects being mistreated?

“These are not abstract questions for philosophy courses or searching editorials. They are real, constant, operational dilemmas,” he said. “Sometimes there is no clear way forward.”

A major terrorist attack in Britain, Sawers said, would exact a terrible human toll but would not bring down British democracy. More far-reaching a threat is the proliferation of nuclear arms, as well as chemical and biological weapons, which have the potential to “alter the whole balance of power in a region.”

He warned of such a game-changer developing in Iran and said that intelligence-gathering was a necessary companion to diplomacy. And for such intelligence-gathering to succeed, secrecy must be at a premium, vigilantly maintained to protect Britain’s agents, its sources and its partners’ confidences.

The need to stay in the shadows is at odds with growing demands for governments to do their business in the open. The pressure for full public disclosure has been epitomized in recent months by the leak of thousands of secret military documents on U.S. military activities in Iraq and Afghanistan, documents that have been posted on the Internet.

But to be effective, Sawers said, “secret organizations need to stay secret, even if we present an occasional public face, as I am doing today.”

Sawers, 55, took command of MI6 last year after a distinguished career as a diplomat, including stints as Britain’s ambassador to the United Nations and as a special representative in Iraq. Within the agency, he is officially known as “C,” just as his fictional counterpart in the James Bond thrillers goes by “M.”