We will spare the blushes (or should that be flushes?) of the lady in question - suffice it to say her unfortunate predicament happened as filming was finishing in West London on a Rainey Kelly Campbell Roalfe/Y&R Powergen ad.
The producer nipped off for a pee in one of the portable WCs provided by the support services company and hooked up to one of its vehicles.
No sooner had she made herself comfortable than the lights went out. The driver, thinking everyone had left, had decided to follow on. Trapped in pitch blackness, it took an uncomfortably long time for the producer to find her mobile and call her location manager, who alerted the driver as to his reluctant stowaway.