Perhaps every time a government minister gets up to bang on about "scientific evidence" we secretly know this: the BSE epidemic perfectly fits Tenner's "revenge effect" scenarios. Why Things Bite Back concerns a philosophical problem bafflingly packaged as a scientific one, with all the familiar jolly eclecticism of popular science on view. It seems the human race has a woeful record in predicting the results of its new drugs and machines, though we continue to act as if we always know what will happen. This is not the astonishing conclusion of Princeton academic Edward Tenner, although it should be, since - after 100 examples of why human ingenuity is perpetually creating inadvertent new problems after the old ones have apparently been solved - he never actually tells us "why things bite back". There is a yet-unknown law of chaos theory which proposes an irreducible number of problems in the world: problems that cannot be solved, only moved around. One of the key developments in warfare in recent years has been less tolerance of casualties - either "enemy" or our own. That means minimising accidental casualties - so-called "collateral damage" - and keeping our own pilots at a safe distance Casom does both. And, unlike the anti-armour weapon, it suits the kind of wars we may find ourselves in Casom would be kept - pounds 600m, not pounds 4bn..

The Nimrods were crucial to the battle with Soviet submarines.The Russians still make some superb nuclear submarines. But the chances we might have to fight a war with them are remote. They also sell submarines to powers with whom we might be in conflict - Iran, for example. But they will not sell their latest and best Akula-class submarines to those powers. Of course, Nimrod 2000 is a great thing to have, and could also be used to track Iranian conventional submarines or blockade runners defying UN embargoes.