Some of the biggest attractions in London have adopted a new trick. They post high admission prices, and beside the price, they now put a little asterisk. Most people don't pay attention to the asterisk, but if they did, they'l see the notice, in smaller type way down at the bottom of the sign that the high price includes a "voluntary donation." The real price is not the one automatically charged.
In this way, the Tower of London costs £21.40 and not £19.50, the true price. Kensington Palace is charged at £16.50, not £15. The Churchill War Rooms look like they cost £17, not £15.45. A few more big guns do it, too.
Americans who already find it difficult to pay the high rates (£21.40 is $32.50 in U.S. dollars, and that adds up on a week-long tour of London) have to opt out of the high price by telling the cashier they don't want to pay the donation, a potentially embarrassing interaction. That is, if they have noticed the overcharge at all. We're talking about some of London's most popular attractions here, and there is nearly always a fast-moving line of tourists waiting to get tickets.
It's hard to be fully outraged about this kind of thing because we're talking about precious architectural rarities, some of them 1,000 years old, all of them irreplaceable, and their preservation is crucial to world heritage. Government funding has dwindled to the point where these institutions seek income at every interaction with visitors. The National Gallery, which has free admission, won't let you pick up a leaflet with a map to its works without receiving £1 for it. There's a sentry who guards the stack of maps like a hawk and politely chastises tourists who dare to take one without donating.
All of the museums also run huge gift shops and cafés, some of the best in the museum world, for the purpose of raising more operations income. So if you're unwilling to pay the "volunatary donation," there are many other ways you can show your support.
It's also true that plenty of American institutions do it, too. The Metropolitian Museum of Art in New York City posts huge signs telling tourists, many of whom don't speak much English, that the entry fee is $25, but plays down the fact this rate is actually only "recommended."
But on the other hand, this kind of sleight-of-hand wouldn't be tolerated in any other industry. If an airline or a car renter were to charge customers a higher price that they had to opt out of, people would be in a fury. It's not good consumer practice.