With all this LHR /British airport mess... is it a rule that i can claim my airport tax for an unused flight? We all know how much the tax is and it does build up if you keep changing ur itinerary.

I've a return CX/ BA metal trip to LIS, half a CX trip to HKG(re-routed but paid for alt airport tax and re-route supplement), and an unused LH trip to LHR from FRA(due to the reroute)

There were threads talking about this but I have yet to succeed in claiming... yet i know it depends on the airline... i guess...