What British hotels are like

No, London hotels don't look like they did in 1883 (and the old Metropole is now the Corinthia). This is what they're like now.

How British hotels differ from American ones

Just keep in mind one overarching factor and you will understand many of the "shortcomings" most American guests find in hotels in Britain (all of Europe, actually): space.

Americans have nothing if not plenty of space. When we think of hotels, we tend to think either of roadside chain motels at highway interchanges or glass tower skyscrapers in city centers.

What nearly all of these have in common, from the swankiest Manhattan Sheraton or Hilton to the humblest Motel 6 in Mississippi, is that they were purpose-built to be hotels—and there was plenty of room on which to build.

That's why even a cheap, grungy, off-brand motel in the States will usually have two double or queen beds in it, separated by an end table with a TV remote control bolted down so you can watch your "Free HBO!"

In the U.K., most hotels—at least, most of those in the historic city centers and small towns tourists love to stay in—are converted from existing buildings, many of them hundreds of years old.

Rooms were smaller back then, and it is often impractical (and, in the cases of historic buildings, illegal) to enlarge them.

Also, indoor plumbing is a relatively recent phenomenon—Georgian architects didn't plan for a private bathroom in every chamber of the townhouse, see. So bathrooms tend to be teensy, modular jobs wedged into one corner of the existing room—there was simply no other way to do it.

So, expect the following from a hotel in the U.K. (and be pleasantly surprised on those occasions when things turn out to be better than expected):

Rooms will be small. No, even smaller than you are imagining. No, really: smaller even than that. OK, now knock off another 20%. There.
Bathrooms will be even smaller (and given to all sort of other "shortcomings") » more
Lobbies and rooms rarely agree. Never judge a hotel by its entrance; expensive hotels almost always invest heavily in the lobby, often skimping on the rooms, whereas cheaper hotels may just have a dingy desk in a hallway, but spotless, fine accommodations.
Beds are a bit narrower than in America. Also, a standard "double room" in Europe comes with a single double bed, sometimes a queen—never two queens side by side with an end table in between; you're thinking of an American motel. Even at that, "double beds" are often two twins shoved together under a single top sheet and blanket (or two twin sheets made up to overlap). Hint: Turn the mattress parts parallel to the springs and you won't suffer from separation anxiety (or end up slipping through the crack) in the middle of the night. In cheap hotels, the beds may have all the spinal support of a wet noodle, bowing deeply in the center on very lazy cot springs, or bulging up and bucking like a bronco every time you stir, dumping you unceremoniously on the floor should you attempt to do something as drastic as roll over in your sleep. Enjoy!
Elevators are a nice bonus, not a given. (Again: Victorian architects were not prescient enough to include elevator shafts when designing the buildings: just lots and lots of steep staircases. Look at it as a chance to get in some more exercise while you're on vacation.) Those hotels that do have elevators often feature rickety, slow lifts that really belong on the city's official register of historic relics.
Walls will be thin. Also, Europeans are an amorous bunch. View it as encouragement: they're setting the bar high and challenging you to rise to new levels of performance.
Breakfast will likely be mediocre—outside of a country B&B. Yes, sometimes they will offer the deliciously caloric Full English (or Scottish) breakfast, but often it's just rolls and jam with tea at worst; more likely packaged pastries and tea—and maybe some fresh pastries. Sometimes you get a table laid out with ham and salamis, cheese, boiled eggs, yogurt, and fresh fruit. Occasionally meusli (a Swiss granola that tastes like slightly sweetened home insulation material) will make an appearance, but don't expect American cereals or omelettes and bacon.
Floors are often tile, wood, or linoleum, not carpeted. Also, Europeans count floors—as in the stories of a building—differently. The ground floor is called the ground floor. Simple enough. But the floor above that is called the first floor (what in the U.S. we'd call the "second floor"), and so on. I know this tidbit has nothing to do with surfacing materials, but it didn't fit anywhere else and it's useful to know.