That doesn't look like rural road in the UK (yellow lines down each side). I drive down rural roads everyday and there are usually no road markings.
Honestly getting past people isn't that much of an issue. There are normally passing spots where you pull over to let people through.
"Chelsea Tractor" is more of a dig at people Range Rovers for the looks and it never been using off-road.
There is a brand in the UK that have decided to "own" the label. Not sure why you would want/need a Ineos Grenadier in London, but some people will buy one.