Originally Posted by
MoreMilesPlease
I believe that Heathrow and maybe Gatwaick have very large airport taxes. These are low if your are transiting. If you skip the last leg and are no longer a transit passenger then the airline may come after you for the extra taxes.
The airport taxes are charged when you leave LHR or LGW. They are not charged if you are transiting or arriving. We are actually coming back from Paris and transiting in LHR instead of flying LHR to EWR. Even taking into account the Eurostar fare we are still saving about $500. in taxes for the two of us and we get to see Paris again.