have to disagree with your take on it. I ride all the time in cities and I also drive a car regularly.
Taking the lane is something I only do in very specific circumstances, but generally feel that what you are suggesting increases the risk to the cyclist, and also isn't a good diplomatic thing to do or considerate for cars on the road who come upon a much slower moving vehicle like a push bike.
on paper or on the internet, taking the lane is a fine idea, but in my opinion, a cyclist also has to be situationally aware of the specifics of a road situation.
Sure, Ive been on narrow UK roads where I had no choice but to impede car traffic, but there are many times when using my mirror and common sense, I just pull over for 5 seconds and let cars or a truck safely go by when there is lots of oncoming traffic also.
for the vast vast majority of my riding and touring years, this has worked perfectly fine and suggesting that one rides a few feet from the edge of the road is not the best solution.
you too might be flexible in your approach to riding on the road with cars, or you may be inflexible in your views, I can't know.
safe riding
If you’re riding in the first foot of the road, you’re hitting every drain grating and broken bottle, so good luck with that. Add another foot or two and you’ve got some space to move in case of emergencies. You take the lane to stop dickheads overtaking you dangerously at pinch points. Yes, by all means shuffle over and let traffic by on narrow lanes if that floats your boat, but realistically they’ll be a passing place at some point soon enough for the driving community to use. Compared to North America, it’s a different style of road construction and use, but it’s considerably safer in the UK than there and the statistics back that up.
This advice is based on commuter, audax, utility and touring riding around the UK between 1986 and 2016. I can also advise that it’s considerably better now than earlier, with drivers in the main being more considerate than in the 1980s and 1990s.
TDLR; North Americans, don’t let the different road style put you off cycle touring in the UK.