> That said BA earned a hell of a black mark when it chose to divert to Heathrow rather than Stansted or even Gatwick when its engine was on fire

After declaring an emergency, if they landed at Heathrow, that was at the pilot's discretion or due to limiting factors like runway length at Gatwick and the weight of their plane. The article is light on detail but they circled over Kent as well, so the pilots must have thought it was safe after shutting down the engine.