A brother, even more analytical and logic-chopping than myself, is planning his first driving trip to the U.K., and wrote to ask for my advice and experience (credentials: six long trips there, all including extensive driving, between 1979 and 2005). I wrote:
1. Some people find driving on the left to be alarming. I did not. The only trouble I had was that I found that my instinctive knowledge of where the passenger side of the car is, in relation to outside objects (as viewed from the driver's seat) did not instinctively transfer over. And since British roads are narrow, with parked cars in unexpected places, and stone walls or hedges often tightly bordering the lanes, it's very easy to hit something by accident. As a result, I always get CDI when I drive in the UK, though I never use it at home. And, at least twice, I've needed it because I accidentally hit something with the passenger side of my car. The first time I drove there, a passing stone wall swiped the passenger side mirror off.
2. Everyone drives very fast. Even many of what look on the map like major highways are single-lane-each-way winding country roads, and drivers dash down at 55 mph on roads that no sane person would take at over 35. And if you drive slower, they'll come up behind you and honk furiously, but because of those stone walls and such, there's often no place to pull over. And if you're behind someone slow, because the roads are twisting, passing takes a lot of nerve.
2a. As a photographer, you'll find this very frustrating. Perfect view, nowhere to stop is a common experience.
2b. It also means it's hard to pull over and look at a map. Signage on country highways is good, less good on back roads. City street patterns are so complicated it's impossible to figure out where you're going without repeatedly checking a map. If you're comfortable using GPS, consider getting it.
3. On the freeways (which they call motorways, and which are very limited access, like turnpikes) and multi-lane highways (which they call dual carriageways), they also drive very fast, but the cops enforce the speed limits strictly. I don't have enough experience to be sure how these facts interact.
3a. But one thing is clear on multilane highways. Always, ALWAYS keep in the slow lane unless you're passing (which they call overtaking). The kind of wandering down the freeway in any lane you like that we have here, with only the vaguest obeisance to the idea of fast and slow lanes, was absolutely unknown there when I first visited the UK, and had barely made an appearance the last time.
4. Despite 2 and 3 above, it takes a long time to get anywhere. The UK is about the size of California, but in terms of travel time it's much bigger. Expect everything to take longer than you were expecting.
5. There are very few traffic lights, and those mostly in large inner cities. Intersections are mostly handled by traffic circles (which they call roundabouts). The British are very skilled at handling these. Rule: when it's your turn, GO. Just go, don't hesitate. If you pause, you'll mess up all the traffic around you.
5a. Same thing applies to stop signs. There basically aren't any. Where the US would have a stop sign where you have to stop and pause and look in all directions despite the fact that's perfectly clear that nobody's coming, the British manage rural and residential traffic with road markings indicating who yields to whom. If you don't yield, you just go. If you have a yield marker but nobody's coming on the cross road, again, you just go. You don't stop and look; you look while you're going, and then you just continue. If someone is coming, you wait for them and then you go. It's much more sensible.
6. Mention of lane markings reminds me to advise taking a prior look at Her Majesty's Driving Regulations (or whatever they're called). Signage is unlike ours, and it's useful to know what they all mean.
7. Her Majesty's gasoline (which they call petrol) grades are also unlike ours. Ask the rental car people what grade of petrol you should be getting. And it comes in pounds per liter instead of dollars per gallon, so it's hard to figure out how much it costs, except that it's over twice what it costs here. (Higher taxes, and it does discourage driving.)
Now, on to your specific questions:
> Where in the UK have you driven to?
All over England, most of Wales, and one venture into Scotland. I've been to Edinburgh, around the countryside south of it, and one quick trip north to St. Andrews. No farther than that.
> - do the rental cars come with stick or automatic?
Unless this has changed since I was last there, almost all rental cars are stick. Automatic has to be arranged beforehand. Right-hand drive doesn't affect anything else: you move the stick with your left hand instead of your right, but first gear is still upper left, etc. Clutch, brake, and gas pedals are also in the normal order.
> - are hotels in rural parts of northern UK just as easy to come by as in
> the US?
No. Motor inns of the Comfort Inn/Quality Inn sort are common enough along major highways and big towns, but not in small towns and rural areas. What I usually did in my roaming-around-the-countryside trips was that early in the day I'd figure out whereabouts I'd want to stop that night, and then go to the nearest British Tourist Office and have them book me ahead a bed & breakfast for that night in wherever I'd be going, which they would do for a small fee. Of course that was before the web, which changes things.
There are 3 kinds of bed & breakfast. B&Bs proper are actually spare rooms in someone's private home which they rent out. I found that idea a little creepy and never used it. Instead, I stayed in the second category, Guest Houses. Those are also houses, but they've been made up as tiny hotels, and are usually pretty professionally run. What they call hotels are usually also converted older buildings; they have all the disadvantage of guest houses (in terms of being old and idiosyncratic) but because they're larger they're also more impersonal.
> - given the population base, is the amount of freeways (or other
> multi-laned highways) similar to that which would be found in the US?
> Greater? Less?
Less. London is a huge city with one beltway (the M25) and virtually no freeways inside of it.
> - Do the hills stay green year round? Or do they change colors
> significantly like in the coastal hills of California?
They stay pretty green. Britain can be wet at any time of year.