Second, I turn to a case such as that of  Tony Bland, the Liverpool supporter who was crushed at the Hillsborough football ground in 1989. He continued to live in the sense that, with the help of a life support machine, he was able to breathe and blink. But the cortical part of his brain had turned to water and I understand that to mean that any form of consciousness was forever denied him. Consciousness was not only temporarily absent; it was forever gone and totally irrecoverable.

Now, in that rare case, it seems to me you have a human being who is living and not. Living biologically yes, but not living responsively or personably. Now, all other considerations apart, I think it would be morally admissible to turn off the machine and terminate life in such a case, but it's a very rare one. Again, I think that we need to be extremely conservative and cautious in judging when human life is bereft of personal capacity, and also to be generous in how we think of personal capacity. I say that we should be cautious not just because by instinct I am conservative, but because the value of human life is so precious. We now live in a society that has been taught to value life in a way that our ancestors didn't, and this has been a historical achievement.

That is a major contribution of Judaeo-Christian thought to Western civilisation. First of all, Christianity broadened the definition of the favoured people from the Jews to the Gentiles. Under the influence of Christianity the Romans stopped abandoning unwanted infants on hillsides. It took until the 18th and 19th centuries in this country and America for Christians to expand the definition of full humanity to slaves, but even in the New Testament you have St Paul urging a slave owner to treat his slave as a beloved brother. 

The point is that the instinctive value of human life that you and I share is not just part of the cosmic furniture, it's not universal. The Aztecs didn't think it was, nor did the Spartans, nor even certain Romans. Our high esteem for human life is a historical achievement and it can be lost. My concern is about cultural degeneration, and I often find that sunny liberals tend to be blithely unconcerned that things can go backwards as well as forwards.

PS: Given my background and the fact that my parents were refugees from the Nazis and my grandparents perished in the Holocaust, I am very well aware of the fact that we can lose this, and that even in what appeared to be highly civilised nations at the heart of Europe, that can get lost. I am not going to disagree with you on that for a moment, there is a grave danger that we need to guard against. The question is, how do we best do that? You have agreed with me that there are some cases where biologically human life is not something that needs to be preserved, and that it can even be justified to end that life. What's important is that we do this on the principles of compassion and concern for others. I agree with you that it should not be done lightly, it is a serious act. However, I think that if we allow people to make choices, essentially for their own lives, in the cases of competent adults who are terminally ill, and allow parents, in what I think would also be very rare instances, to make decisions for their infants who are severely disabled, that is consistent with an ethic that says we are deeply concerned for everyone. We are acting out of care and concern for them, and not from a state ideology  that says that certain races or other groups of people are useless or evil.

NB: In Christian tradition there has always been freedom permitted for individual discretion, and that's what conscience is about. There is a certain conscience which is bounded and Christians have been happy for some time to say that if you are terminally ill and in great distress, it is up to you and your conscience to decide whether this or that treatment is going to be too burdensome for you. Even if the treatment might save or prolong your life, you may refuse it if it is too burdensome. It is up to you to judge.