I've been in country for 8 days now. I am using Komoot to route. On the continent I just plugged in the destination and it always found a decent route. In England I did the same and it consistently sent me to the closest high speed "A" road, which I didn't know or notice. Now I plan (when I can) the next day's journey like Eisenhower planned D-Day. I go over every stretch and add waypoints galore to avoid the main roads. The last couple of days I have been following the Sustrans cycle route 5. I have managed to stay off the main roads and it has been much less stressful and way more enjoyable. Of course I'm wandering all over the countryside instead of a straight shot to wherever, but that's ok since, for me, it is the journey, and not so much the destination. Having said that there are places I won't be going to since there does not seem to be alternative (little roads) ways of getting there. But, it is what it is, and you just have to adapt to the local conditions as best you can.

PS Concerning taking over a lane, I get it: I observed that the local riders do that. But at least they are going 15-20 mph. On a hill with my panniers and Bike Friday I'm doing 2 mph. So my current strategy is to just try to stay off those roads as much as humanly possible. As I said before the drivers, for the most part, have been very courteous in their dealings with me.