What I meant was:
In the good ol' days you saw an item displayed with a price, bought the item or service paid the chap and left.
A lot of (legal) effort was put into making UK shopping transparent.
Somewhere along the line this government have changed some rules, as mentioned previously probably to do with tax fiddles, such that just by hiving off the till to a subsidiary company which only exists on paper, the chap can now legally charge more for providing the same service.
So you see your item at X buy it from the chap who gives you an imaginary invoice and points you at the till he is standing at, which is now owned by a subsidiary wholly owned virtual company who now want you to pay X plus Y admin fee for settling the account. And they can now do this legally. It is not the courts that make the laws they just uphold them.
Apart from that, as I see it, due to TO takeovers there is less competition this year which will enable all the companies to jump onboard. These make believe exchequer companies are only virtual, they exist on paper or as entities in an accounting system and the travel companies functions are already divided. You make your booking and any payment enquiries are dealt with by accounts, who have to pass you back if you have any other matters. It would be very simple for them to take the lead of the supermarkets and reduce the bill by the correct percentage so that they can add it back on as an admin fee, or it would be just as simple to get greedy as BT have and add a random amount on.
BTW this is NOT the cc fee adjustment, but that is used as an excuse by some to justify the charge.