100,000 plastic bags
"When I arrived at my tube station this morning at 9 o'clock, the station already had a detailed printed poster with advice about the security alert at Heathrow and other transport. I cannot believe that TFL knocked this up in a couple of hours. Pre-prepared or what? How long had the authorities known this was going to happen? Would the police really tell the tube if this was a real terrorist alert? I will be interested to see how many of the arrested will be convicted. Another Blair PR stunt?"
As Postman Patel points out, quite a coincidence that Heathrow Airport just happened to have on hand tens of thousands of clear plastic bags for passenger carry-on.