The technique, also used at Heathrow, is an alternative to the unpopular method of racial profiling and concentrates on behavioural patterns identified as typical of suicide bombers. Spotting suspicious travellers on the tube seems to have become a national pastime with the Met urging the public to do counter-terrorism on their behalf. Although one of the 'suspicious behaviours' identified is clutching your bag tightly and refusing to be separated from it which at least reinforcesTfL's incessant exhortings not to leave our bags unattended lest they be taken away and destroyed but may result in you accompanying your bag as it's taken away by the security services.
The Mexican standoff between civil liberties and anti-terrorism continues unabated as ever-increasing security measures are rolled out, despite the recent ruling over stop and search. On the tube, this latest (and admittedly less intrusive) tactic joins dogs, x-ray machines and CCTV in TfL's armoury, though we hope that reading body language has become a finer art since 2005 when Jean Charles de Menezes was shot for 'acting suspiciously' on the tube.
In the meantime, tube travellers are advised to make eye contact, don't clutch anything in your pocket and always wear clothing appropriate to the season. Oh, and don't look nervous.