That aeroplane would also be urgently needed for its next service out of LHR. It has missed its flight out of JFK. You can't just delay and operate another service because another aeroplane would already be on a rotation out of LHR, and you cannot for licensing reasons just operate an extra service. Very often the only answer is to bring it back empty. Funnily enough, the schedulers do know what they are doing (but not always).
The word on the grapevine is that the two passengers were travelling with the crew. Smoke down the back........I hope it's not what I'm thinking......crafty fag.......smoke alarm........but then it's only conjecture. All in all.......(sucking breath in through teeth)......someone in trouble.......lies being told......'not me Guv!'