I believe it is well known and discussed that Britain imposes an exit tax on departures from the UK, a tax that is much higher if the flight is in business class. Suppose it is only the second part of the flight, ORD-SAN, that is upgraded. Do they still impose the luxury tax?

Earlier this year we were charged a French luxury tax on LYS-BRU-ORD-DTW even though the only upgraded segment was BRU-ORD. Enough to make even this Francophile think twice about future travel destinations