Thanks Iain for this informative and enjoyable link, and to your readers for several illuminating comments. Your post prompted me to read more into the background of the issue, and I feel I understand it a good deal better.
Why I don't support torture and rendition
I confess to being agnostic on rendition and torture: It would take a lot to convince me that the UK should be complicit, and nothing I have heard has yet persuaded me that we need to compromise our commitment to treat people humanely in order to protect ourselves from attack.
Why I might support it
I cannot, however, confess an unshakeable commitment to the human rights of actual terrorists, in possession of mission-critical intelligence that would save innocent lives. If - and it's unlikely the evidence could be presented in an open forum - I could be shown that methods of torture had a proven track-record of extracting such intelligence in a proportionate way (i.e. with extremely low yield of bad intelligence, extremely low (though not zero) incidence on torturing innocent people, and a strong track record of averting disaster) I must admit I would probably support it.
And why that doesn't make me feel good
I find that admission troubling, and am fully aware of its implications, but hypothetically I'd rather live in a country where my government was willing to make that kind of morally difficult choice, than one in which they exposed us all to greater risk, in the face of clear evidence that they could keep us all safer by victimising a small number of guilty individuals who were intent on ending our lives and bringing down our society.