Have you ever heard MPs bleating like sheep in the chamber? Many years ago, as parliamentary sketchwriter for The Times, I was astonished at the sound from the Labour benches when a little-known Tory backbencher rose.

“Baa, baa!” rang around the chamber. My colleague whispered the explanation. This MP had been convicted of cruelty to sheep, having been legally responsible for his farm employees’ failure to feed his flock. His name was Quentin Davies, who defected from the Tories this week.

David Cameron must now count him a lost sheep. Never mind, these are win-win situations. Every time a Conservative MP crosses the floor to join Labour there is a small but measurable increase in the average IQ of both parliamentary parties.

One of my llamas died last week. He was only a week old. I had found him in the field, unable to feed because he could not see. His eyes were horribly swollen. It was New Forest eye, a fly-borne infection of sheep and cattle. Carrying him inside to keep warm, I called the vet. Days followed of applying ointment every few hours, while I tried to hand-feed him with goat’s milk in a baby-bottle. It was no good. He wouldn’t drink properly, his mother rejected him, and he couldn’t see.

Yet he put up such a struggle to live. I am not sentimental about animals but when he died I was stupidly upset. I think this was because it was I who found him and he had become my charge. Things, tasks, animals, people throw themselves on your mercy sometimes; and ties and responsibilities spring up quite unbidden.

It is odd that neither Christianity nor its founder has anything to say about gradation of responsibility according to relationship. Jesus half-suggests there should be no gradation, consideration being due equally to all. But you can’t love your neighbour as yourself; you can’t even love your neighbour’s cat as your own. Yet we are brought up to think there’s something illogical about tending to the bird that flies into your window pane, then eating chicken that night. Our national religion is completely silent on what is probably the most recurrent, agonising and important area of moral choice.

Chatting with me a few days ago, Norman Tebbit described an unexpected approach from a very senior and slightly embarrassed parliamentary colleague: “I’m writing your obituary for The Times. Could you help with it?” “My dear chap, I’d be delighted, but on one condition: that we introduce into the obituary one small but identifiable error of a kind which The Times will be unable to spot. Then we hand to a third party a sealed envelope containing – for dispatch the day the obituary is published – a letter from me, handwritten to the Times Letters Page. It will begin: “Sir, Even from beyond the grave I must hasten to correct . . .” To Lord Tebbit’s disappointment his colleague turned the idea down.

Easy to imagine: a prime minister serves for years while the rival everyone considers his natural successor waits for the handover with increasing impatience. At last the moment comes . . .

It comes in April 1955 when Anthony Eden gets his chance. First, though, the man reluctantly handing over to him, Winston Churchill, gives a farewell dinner for the young Queen Elizabeth at No 10. In white tie and tails he meets her at the door.

The party over, he climbs the stairs for bed, deflated. Here’s how John Colville, his private secretary, describes the moment: “I went up with Winston to his bedroom. He sat on his bed, still wearing his Garter, Order of Merit and knee-breeches. For several minutes he did not speak and I, imagining that he was sadly contemplating that this was his last night at Downing Street, was silent. Then suddenly he stared at me and said with vehemence, ‘I don’t believe Anthony can do it’.”

Private secretaries don’t pad behind prime ministers into their bedrooms these days. Only Cherie Blair will have been privy to her husband’s departing thoughts on their last night at Downing Street this week. I wonder what they said.

Meanwhile yesterday, outside the same address, Gordon Brown was facing the cameras with a few words for the nation. He would always remember his old school motto, he promised: “I will try my utmost.”

When or if his day comes, David Cameron could do the same. I can just see him on the Downing Street steps: “I will always remember my old school motto: Floreat Etona.”

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