"Obama has been criticised, in particular by Cheney, for making public four secret Bush administration memos detailing interrogation techniques approved for use by the CIA, including waterboarding. Cheney has called on Obama to release other classified documents he claimed would show that valuable intelligence was gained from detainees interrogated in this way.

"Obama responded by pointing to the example from the Blitz: "I was struck by an article that I was reading the other day talking about the fact that the British, during world war two, when London was being bombed to smithereens, had 200 or so detainees. And Churchill said 'we don't torture', when all of the British people were being subjected to unimaginable risk and threat. And the reason was that Churchill understood you start taking shortcuts, and over time, that corrodes what's best in a people. It corrodes the character of a country.'

"Obama said he had read the classified material mentioned by Cheney, but this did not answer the question of whether the information could have been obtained in another way and whether use of these techniques made the US safer.