London cyclists know better than to park their bikes on railings near the Houses of Parliament. They'll be carted away by the police because they could be that favourite terrorist device, a pipe bomb.
(These railings down the end of Whitehall were festooned with bikes during last year's Skyride, when the road was briefly shut off to traffic, and gives you an idea of JUST HOW LETHAL things could be.)
Which raises the question: how many bike-bombs have there been in the history of terrorism?
Note that we're not talking suicide bombers on a bike, or bicycles used to carry a bomb in a basket or strapped to the frame. We're talking pipe bombs: explosives hidden down inside the tube and left in an apparently innocently parked machine for later detonation.
Well, the answer - according to the researches of John Adams in his blog this year - is, yes, you guessed, zero.