The use of torture is "wrong and never justified", the former head of the security service MI5 has insisted.
Eliza Manningham-Buller said it should be "utterly rejected even when it may offer the prospect of saving lives".
"No-one could justify what went on under Gaddafi's regime," she added.
Baroness Manningham-Buller's lectures examine the issues of terrorism and security on the tenth anniversary of the 9/11 attacks on the United States.
She said that the use of torture had not made the world a safer place, adding that the use of water-boarding by the United States was a "profound mistake" and as a result America lost its "moral authority".
Allegations have recently emerged that the Secret Intelligence Service (MI6) was involved in the rendition of Libyan terror suspects, following the discovery of papers suggesting close ties between MI6, the CIA and the Gaddafi regime.
Baroness Manningham-Buller, who was director-general of the security service MI5 between 2002 and 2007, stated that she "would like to say more" on the recent allegations.
However, her position made it difficult to do so as she anticipates being called to give evidence to the Gibson Inquiry which will investigate the subject.
Sir Peter Gibson is chair of the ongoing detainee inquiry, which was set up last year by Prime Minister David Cameron to investigate the alleged involvement in torture by UK security agencies.
A statement issued by the inquiry said it would also be considering the new allegations of UK involvement in rendition to Libya. Some of the inquiry will be held in secret to protect intelligence sources and methods.
Following the lecture, which was held in Leeds City Museum, Lady Manningham-Buller answered questions posed by members of the audience.
The Conservative MP, David Davis, asked the former MI5 head if she thought Britain's resistance to the use of telephone intercept evidence in court had hindered the conviction rate of terrorists in the UK.
Baroness Manningham-Buller replied that MI5 had first suggested the use of intercept evidence in 1988, and she would "still like to see that happen" - but successive British governments have found the idea "procedurally difficult".
The second of Eliza Manningham-Buller's Reith Lectures, which is entitled Security, will be broadcast on BBC Radio 4 on Tuesday, 13 September.