Originally Posted by
KARFA
you can tell them but they are under no obligation to protect the GIG-LHR flight. they may do out of a gesture of goodwill, but they may not. also it is possible even if they say they will the auto-cancellation happens anyway and you would be at the mercy of the agents to reinstate your ticket.
seems your best option is to change the booking.
This is all just theoretical at this point. Just trying to understand if there's an operational or security reason why they won't let you forfeit the first leg without cancelling the whole itinerary? I'm not arguing just trying to understand it.