Originally Posted by
family friend
Oh, really? I was unaware of that! If I fly DUB-LHR on EI and then LHR-JFK on AA and upgrade the LHR-JFK I am not liable to pay the additional tax? I thought since the upgraded itinerary began in LHR I was.
Not liable as long as all on one tix, but buying on one tix might be more expensive than buying DUB/LHR on EI on a separate tix. You will have to run the numbers