Originally Posted by
3Cforme
By fare rules, that is not a layover in London, it is a connection in London, at less than 24 hours. That distinction is important in trying to avoid UK Air Passenger Duty, which, in Business LHR-JFK, would be significant.
That's a good way to enjoy the 77W but you haven't exactly discovered fire.
To avoid APD when connecting through the UK the two flights must also be part of the same trip. The definition is not 100% clear, but if they are not actually on the same ticket number then you may have to show that this was because there was no option to do that and that the two flights were booked at essentially the same time.