Iirc, 1985, PA flight SFO-LON. The cockpit crew were issued an abort message and performed a high-speed taxi on the active runway back to the terminal. We unloaded pax and baggage, and watched the dog get very twitchy at an uncollected bag turned in by a chap who had checked in at the podium and departed, when we collected and rechecked our luggage. (The bag was deal with by the SPD EOD team.)

This was after we were counted and recounted, and checked onto the aircraft at least three times before being cleared for departure. Someone had the brass to risk his / her job and cancel the flight departure for further screening. ^

Four hour delay - no complaint from these pax.