Speaking of Driving...

Your options would be...

1. Pack lighter, bring smaller/fewer bags.
2. Rent a larger car.
3. Bring fewer people along (this may the most problematic of your options...).
4. Rent more than one car. Hmmm.

Option #2 seems the most realistic (I mean, pack lighter/smaller bags anyway, but there are limits to what you can expect from people or a car). Rent the smallest car that meets your needs. Then drive v-e-r-y carefully.

We already plan to pack very light, with a single carry on bag per person.
And none of us is staying home.

What I'm asking is, from those who have actually rented these options there, how did it work out? Is the compact SUV considered small? Small enough for narrow country roads? Did you all have to hold your luggage in your lap?

Have rented in Scotland (tiny roads), but not England, although there will be 5 of us together in Italy for a week in October. Everyone’s arriving by train, then splitting up after that week, so we won’t be toting around luggage in the car, and a compact will work.

Last year, just 2 of us - with luggage, got unexpectedly upgraded to a Ford Puma compact crossover/SUV. The covered hatch storage compartment held our 2 international carryon sized suitcases, plus 2 day bags. Could’ve held 3 suitcases, but not 4. We did have the back seat open to toss in jackets, umbrella, or to keep backpack handy. And having everything hidden in the back hatch, under the cover, was easy.

With a smallish SUV, maybe you could fit in 3 suitcases, and strap in the fourth inside the car, between the two people in the back seat. That might be acceptable, or too cumbersome. Still, I doubt you could keep everything out of sight if you parked for a while. Much bigger sedan or SUV with a sizeable trunk is probably needed, for 4 people and stowable luggage. Maybe minivan?

In Scotland, medium cars got on the tiny roads going both directions, but there wasn’t a lot of extra elbow room on the road. Don’t drive too far left, avoiding vehicles coming the opposite direction, to risk running off the edge. There were relatively big campers - many with Belgian and Italian license plates, and they had a tough time staying on their side of the center line -driving their personal vehicles from the “wrong” side of the front seat, and on the left side of the road. Huge is too big, but medium might be what you’ll want, at a minimum.

" Much bigger sedan or SUV with a sizeable trunk on s probably needed, for 4 people and stowable luggage."
Cyn- that's what I was thinking, but then I see so many comments about "two lane roads that are more like one lane", and so many warnings of "get a small car" that I worry that the car that would fit our needs will be problematic in actual use. But at the same time, I'm sure not every person who owns a car in the UK has a compact. Surely there is room somehow, right?

I just expanded my earlier post, maryellenhowen, and corrected some typos, so please reread it, and sorry if it wasn’t fully proofread to start. Some of the changes did include some of what you just mentioned, but I’d say you’re right - smaller is better. However, get only as small as you can use. Roads aren’t so tiny that only a motorcycle can get through. You probably won’t want/need the biggest Jaguar, BMW, or Jeep available, but one size up (maybe two) from “compact,” especially with cost factored among 4 occupants, would be where I’d start looking.

A Ford Focus will hold two suitcases in the boot (which is what they mean by bags) so you may get four carryon bags in that space. A Nissan Juke is a bit bigger - would probably hold three suitcases. But if you feel you'll need more space, just go for a bigger car. We've driven larger SUVs on country roads without problems, both in England and Scotland. We generally have several suitcases, and often opt for an estate car, because it has the space, but is narrower than an SUV.
If you're not familiar with the car, it's worth doing a quick Google search. There are numerous YouTube videos where people demonstrate the size of boots, showing how many bags they can take. One thing to watch is that some of the compact SUVs, while bulky, have similar boot space to a standard sedan.
On driving, we found even in the Scottish Highlands the roads are fairly easy to navigate. Some narrow ones mean you need to give way to opposing traffic crossing smal bridges on single lane roads.

It's been a minute, but when we had our week driving the Cotswolds and environs, we had rented a Ford Focus, but we were upgraded to a 4 door Mercedes sedan ( mid size). Yes, some of the country roads were very narrow. No we didn't have any problems. We found the trick was to drive slowly when approaching or entering a blind curve. We did have to stop rather abruptly a couple of times for sheep on the road, and there was one time when we had to back up a ways to allow an oncoming truck to pass by. Just don't expect to set any land speed records.

If your driving is all going to be out in the countryside, I don't think car break ins will be a big problem, but all you can do is take whatever precautions you prudently can.

A number of years ago we (4 adults) did a road trip in Spain, in what would definitely be called a compact or even economy car in the U.S. Each had a 22” suitcase and a small carry-on. I think a couple of the carry-ons were under the feet of the passengers. We managed without too much discomfort. The problem is that you get no guarantee of what model car you will receive, just a category. Certainly some will be more comfortable than others.
The other question is what is meant by “2 bags,” or any other number. 21 inchers? 26 inchers?

Whereabouts are you driving? Devon & Cornwall have some very tiny single-land roads with passing places, but by no means all of the English countryside is the same.

You have multiple issues here...

1. Be aware that when the rental companies give you info about a car, that is NOT necessarily the specific car you will get (and very rarely is). Note, it will say something like "Nissan Juke, or similar", "Ford Focus, or similar."  You can go look at a Nissan Juke and that may give you a general sense of roughly how much room it has, but you will get the car they have available for you, probably not a Nissan Juke, so don't count on one. You can generally go by what they say it can hold, eg 5 adults + 2 bags (of course, it depends on the size of the bags...and the size of the adults!).

2. Trunks/boots tend to be smaller than you would like, so the "security of your bags" conundrum will remain. There is no perfect solution to keeping lots of luggage out-of-sight unless you end up with a giant battleship-class US car (which is highly unlikely). You are going to have to make some compromises, one way or another. The "I want all my bags safely hidden in the trunk" one is a tough nut to crack, even when traveling as a couple.

3. Yes, many roads in the UK are narrow, sometimes shockingly, impossibly narrow. And parking is a PITA. So yes, you want as a small a car as possible, but it also has to meet your other needs. So, strike a balance. And get good (quickly) at driving on narrow roads, because your driving skills will soon be put to the test (and you have skin in the game -- literally).

4. No, not everyone in the UK drives a tiny car. They make do. Yes, there is some room, but sometimes that "room" is a impossibly skinny lane just wide enough for a tiny car, with occasional "turnouts" or wide spots. You probably won't be on any of those for long, but if you encounter one, you need to be prepared to give and take. You may need nerves of steel when you see an oncoming truck and it seems there may not be enough room for you both (there may not be!). The driver needs to take driving seriously (deadly seriously...) and others in the car need to help with spotting your position, how close you are to the curb (or stone wall..), all navigation tasks (pointing out signs and which places to turn, etc.), supporting the driver rather than distracting them -- offloading every non-essential task so the driver can concentrate on just driving safely. Driving requires care -- be sure your driver is up to the task. It can be stressful -- take breaks, stay fresh, let the driver be on her/his "A Game."

It gets easier with some experience. Be extremely careful in the first hour you are behind the wheel -- I once witnessed an American couple at a UK car rental agency jump in their newly rented car, drive off, and total the car in a head-on collision right outside the car lot, having driven no more than 100 meters. (I was still completing our rental paperwork -- the staff shot me quite a look when we all heard the loud crash when the previous customers smashed their car...).

Just get a bigger car--if you are doing a lot of driving, you don't want to be crammed into a tiny compact anyway. We've rented a mini SUV type car in Ireland and in Italy, where there are certainly narrow roads and tiny towns to drive through, and it was fine. I thought my husband was crazy, but he is a very good driver, and when we were driving through pouring rain, I was actually relieved to have the larger vehicle.
If a thief wants your luggage, they know how to get into the boot anyway, so you just do the best you can. That warning gets repeated about certain areas (like Pisa for example), but I would not particularly worry about it in the English countryside.
Just google the car model--you can get pics and video and trunk specs, etc.

We drove through some of the tightest roads in England, Wales, Scotland and Ireland in our "Spaceship", a Toyota Tarago. We also lived in it for 7 weeks, sleeping in the back.

My best mate did the same for 5 weeks a couple of years later, their Spaceship was a VW Caddy. Two of my friends from that trip of ours are Munro (Scottish peaks) bagging as we speak while living in their VW Caddy.
I drive a a 5 seat diesel VW Caddy (with windows next to rear seats) at home. It typically has a kayak on the roof a road bike and a mountain bike, spare bike wheels, camping gear, kayak gear, half my wardrobe and a wide array of footwear in the back.

If I was planning on a similar trip to yours the 5 seater Caddy would be my choice of vehicle. The model with rear seat windows so everyone has a view. If not available then something very much like it.
I don't know the Juke (not a car buff) but will google it now.

The Juke looks OK but doesn't have a lot of boot space for 4 people' luggage.

What you reserve and what to get upon arrival are not always the same. You’ll get what’s available when you arrive. Sometimes it is what you reserved, most of the time it isn’t. To help me determine the vehicle to reserve, I search on luggage capacity for the car referenced on the rental company’s website. I can compare that number to a known vehicle we either own or had on a previous rental.
While some rural roads can be narrow, we’ve never had an issue, and there are some really narrow rural roads in Wales and Cornwall. Reserve the size vehicle that will meets your needs.

If you are not sure about the names of cars in Britain and how big they are, this site will tell you:> https://www.parkers.co.uk

Thank you all! I feel much better now with my earlier plan of getting the size we need. My husband (who will be driving) pointed out that it isn't much different than the neighborhood streets in Seattle where there's only room for one car at a time in between all the parked cars. I will look more deeply into the various models that each category contains, knowing that a specific car is not promised, but just a specific size/style.
For those who asked, the driving will be:
Bath>Wells>Glastonbury>Salisbury>Cotswolds>North Wales (Conwy/Caernerfon)>Lake District (Ambleside/Keswick).

Other than possibly a couple roads in the Cotswolds, your husband should have no problem.

isn't much different than the neighborhood streets in Seattle where there's only room for one car at a time in between all the parked cars.

true, but in Seattle the speed limit on single lane roads in the country isn't 60 mph. With vehicles coming at you at considerably more than you'd do in a neighborhood in Seattle (I guess).

You just have to have your wits about you and be ready to instantly respond and look over the hedges and around corners for hazards - as well as cars and trucks, livestock, horses (pass WIDE and SLOW), pedestrians, bicycles, sometimes in peletons...

When rental agencies mention bags they are referring to an average sized suitcase. There are very few cars, if any, that would not accommodate four carry-on bags. A Nissan Juke or similar will be fine.

We did a four week drive tour of South Wales and England in 2017 and had two checked bags with two carryons. None of the compact cars suited us. We had to rent a larger vehicle, which cost more, but it was worth the cost.

No way was I going to leave anything visible to the public in my parked auto.

Also, we rented an automatic. I didn't want the extra issue of shifting gears with my left hand to distract me, as we had to drive on the left.