Originally Posted by
BrianWBrazil
So, even though (through some mishap on your tour) you are geographically closer to LHR on the day of the flight and could easily mitigate the entire loss by getting to LHR on time, you are still obliged to get to MAN and take that flight. Okay, that's clear, thanks.
That's where you've bought the flight from, so yes. It'd count as a no-show otherwise. Unless you can contact BA and make a change - but this will likely cost you more money than getting a train to MAN.