There's something about nomads, travellers, gypsies and tinkers that disturbs us respectable stay-at-homes. It's deep in our belief systems, this anxiety, and goes beyond the rational suspicion that if you are going to be encamped on the horizon by tomorrow's sunset, you are beyond vendetta, you will have nothing to fear if you dally with my women and steal my hard-earned treasures. When I was last in Zambia, in Lusaka, there was a new conviction that crimes and nuisances, tears in the public fabric and insult to the body politic, formerly attributed to taxi drivers and other resident criminals, had suddenly become the work of the Somalis; the Somalis being an encampment of maybe a hundred and fifty destitute and timorous refugees down by the market. They were no doubt up for a bit of stealing, these Somalis, how else should they live? But they certainly didn't have the logistics, the numbers, the fire power or the energy to accomplish one percent of the wickedness carelessly attributed to them. And when foot and mouth disease struck Britain and decimated the sheep and cattle population a few years ago, a Northumberland farmer's wife wrote a column in the Guardian, describing in workmanlike but heart-rending paragraphs what effect this scourge had on farmers and their families. Only once did she entirely lose her cool, right at the beginning of the outbreak. She described how a lone mountain biker had ridden across the county, along footpaths closed by Defra, spreading the risk, almost the certainty, of cattle annihilation as he went. So subtle had been his subterfuge that he had closed all gates behind him, moving like a shadow; in fact nobody had actually seen him, this spectral traveller. The only undeniable evidence of his passage had been tyre tracks, mountain bike tyre tracks, the tread pattern unmistakable and always the same, reported from every corner of the county. So that was that then. It wasn't the squalor of farming practices, the incompetence of Defra, the idiocy that reigns in Whitehall and at Westminster that brought the plague upon good country folk. That would be too complicated. No, it was an invisible nomad, a lone mountain biker. The American artefact of Al-Qaeda follows the same pattern. That the interdependencies of interest and relationship among Saudi Wahabis, the Pakistani Inter Services Intelligence agency, the poor and dispossessed who struggle to survive the thuggery of the US-Israeli axis, and a hundred other islamic groupings; that all these might be the complex cause of falling towers and exploding trains, is unnecessarily complicated for White House and Pentagon purposes. No, keep it clean. Blame the global nomads.