Without commenting on whether anyone should legally challenge Thai Airways, should any of the affected people desire to do so a starting place would be to investigate whether all of the 55 pounds or so collected was LEGALLY collected as collecting agent for a government or whether some of the 55 pounds was to reimburse the airline for fees, etc. legally imposed on the airline by a governmental entity. If some of the 55 pounds went to the airline to reimburse it for fees or costs legally imposed on it (or were separate fees imposed by the airline), you may have paid consideration. The clearest example would be if a "fuel surcharge" or "paper ticket fee" were part of the 55 pounds. Even though stated separately, under many legal systems, the ticket fee or fuel surcharge would be "consideration."

The other extreme is where the tax or fee is imposed directly on the passenger by a government, but the airline is required to collect it as a collecting agent. Where the airline's legal role is merely a collecting agent, one would have a harder time finding consideration.

One would have to look carefully at the legislation to see whether the tax was imposed on the airline or imposed on the passenger. I do not know whether class actions are available in the UK, but that might be a good question to ask a UK barraster or solicitor.