On my Chase visa (United airlines) which says it covers rental car insurance, it says to check with the program manager to see if coverage is provided in the country you are renting in.. I have no idea what this means.. and as I am going to the UK for a month this Summer I intend to check it out with Chase.
As I am English, maybe they will insure me on the other side of the road.
Oh remember lane discipline is enforced, passing on the inside is not permitted and travel speeds are tolerated up to 90mph on the motorways (or at least it used to be).. Move to the slowest lane available, that would be the left lane... Or you will get some very unhappy people behind you!