Apparently that's why they did during our strike in 1997.
Hi Miss M. That might be so, i can't recal at all to be honest. However, in the modern day, theres no way ATC would permit empty planes just to fly around LHR. It would cause absolute havoc. I think you've guessed it anyway, but its simply another BASSA sensational headline intended to whip up and bhuoy the masses.
There were, however, a handful of empty flights that took off for repositioning purposes and crago freighting but these are well documented in their own right.