MI6 boss: 'Nukes are key threat'

Britain's top spy has claimed that terrorists might hit the West again "at huge human cost" but nuclear proliferation by states was a more far-reaching danger.

in the first public speech by a serving UK espionage chief, Secret Intelligence Service head John Sawers said the risks of failure in tackling proliferation by countries like Iran "are grim".

"Terrorism is difficult enough, and despite our collective efforts, an attack may well get through. The human cost would be huge. But our country, our democratic system, will not be brought down by a typical terrorist attack," he said.

"The dangers of proliferation of nuclear weapons and chemical and biological weapons are more far-reaching. It can alter the whole balance of power in a region," said Sawers, whose century-old service is popularly known as MI6.

Sawers defended MI6's secrecy and its ties to counterparts in Muslim nations accused of poor rights records, a theme that has resurfaced in the West after the whistle-blowing Wikileaks website published secret U.S. files it said showed how coalition forces turned a blind eye to torture by Iraqi security forces.

"We are the secret frontline of our national security," he said. "Secrecy is not a dirty word. Secrecy is not there as a cover up. Secrecy plays a crucial part in keeping Britain safe."

"We have to deal with the world as it is ... We can't do our job if we work only with friendly democracies. Dangerous threats usually come from dangerous people in dangerous places."