This is actually BA doing pretty well for their passengers.

The Miami to London was diverted to Boston for a medical emergency on board. Given the normal eastbound routing for Miami flights it was probably well out over the Atlantic when this happened, so a significant diversion.

Getting the emergency off and into the ambulance, and their bags off, they did pretty well to turn round in an hour in the middle of the night. Now they have a planeload of passengers and a crew with just insufficient hours to get to Heathrow legally. They could have laid everyone over in Boston for 24 hours, but instead carried on to the best available point that balanced crew legal regulations and proximity to London. They are just not allowed to flight-plan the new flight from Boston to London if they don't have the right number of hours available. And so they all got to London as promptly as possible. Places like Prestwick would be much further away. Cardiff is only a couple of hours down the motorway.

I'm sure some poor passenger in a hospital in Boston is pretty grateful for all the organisation going on handling this at Waterworld in the middle of the night.