Mr Science Notebook once offered an incisive analysis of conversation with the Ahujas. “You all argue for ages before realising you’re saying the same thing,” he sighed. “Then you argue about who said it first.”

Thanks to a lifetime of practice, I am now perfectly capable of debating with myself. This is the case whenever the question of Brits in space arises. Last week the Commons Science and Technology Select Committee published a report on British space policy. Among its considerations was whether Britain should have a manned space programme.

As a former space scientist, I cannot justify manned space travel. It may lift the spirit of a nation to see its citizens blasted into orbit, but it is enormously expensive, risky and wastes cash that could be more productively spent on robotic explorers. Robots can operate in environments that would freeze, fry or suffocate human adventurers, don’t need feeding and are dispensable. They cost mere millions; Nasa’s human spaceflight programme costs £6 billion annually.

But, I reply (to myself), the thought of dispatching metal rather than man into the great unknown is depressing. Shouldn’t science be about inspiring the young and transcending the humdrum? Isn’t it dispiriting that bean-counters expect space missions to be symbols not of valour but of value for money?

Actually, not having a manned space programme saves us the embarrassment of British astronauts. We have only one: Helen Sharman, who flew in 1991. The other “Britons” - the Nasa astronauts Michael Foale, Piers Sellers and Nicholas Patrick - are actually British-born American citizens.

I once sought to interview Sharman; she refused, saying she had “moved on”. Perhaps she was having a bad day but I thought her ungracious. What a contrast with Colin Pillinger, the British professor, who, even as his beloved Beagle 2 was plunging to its doom on Mars, always found time to smile for the cameras. There is an insightful piece in the latest New England Journal of Medicine by the psychiatrist Simon Wessely, on doctors and terrorism. He wonders, as I have done, why Britain is so shocked that doctors should aspire to be mass murderers. Rather, he asks, why should doctors not become terrorists?

Modern history is crawling with examples of physicians who have turned their healing hands to hate. One architect of the sarin nerve gas attacks on the Tokyo subway was a former heart specialist. Radovan Karadzic, the Bosnian Serb leader and suspected war criminal, is a psychiatrist. Osama bin Laden’s deputy is an Egyptian surgeon.

Doctors must, for their own sanity, be able to detach themselves from suffering and death. They possess self-belief. This makes them even more dangerous if their minds are perverted. As Sherlock Holmes told Dr Watson: “When a doctor does go wrong, he is the first of criminals. He has nerve and he has knowledge.”

Times Recommends

• You created the job. You should do it
• A swindler with a ready maid plan
• Charming to pillory disabled Brown