The number of British airports with security body scanners is now being doubled, from 10 to 21, in response. Three years ago, a bomb sent from al-Qaeda in Yemen was found on a plane at East Midlands airport, disguised inside a printer. Another reached Dubai airport. Since then, a further device was discovered in Yemen in May 2012. So just how serious is the threat? In the airline security business, they call them Artfully Concealed Devices: sophisticated bombs, mostly non-metallic with a hard-to-detect, “low-vapour explosive” like pentaerythritol tetranitrate (PETN), disguised inside ordinary, harmless items like shoes, underpants, soft drink bottles or even printer ink toner cartridges. Three times al-Qaeda’s franchise in Yemen, known as al-Qaeda in the Arabian Peninsula (AQAP), was able to evade airport security and smuggle bombs on board planes in 2009 and 2010. Now Whitehall officials believe they are trying again. Little wonder that of all al-Qaeda’s branches around the world, AQAP in Yemen is considered to be the most dangerous to the West. “The most serious terrorist threat to European aviation comes from AQAP,” said a senior counter-terrorism official who asked not to be named. “They are technically adept, they move very fast, they have a core of experienced people, they operate in a country with fragile areas and elude the Yemeni authorities. Plus they have the ability to inspire people to lone acts of terror.” Al-Qaeda in Arabian Peninsula airline bombs August 2009: AQAP bomb-maker Ibrahim al-Asiri sends his brother from Yemen to Saudi Arabia…more detail