I don't normally pass, unless it's dual carriageway. It much depends on your outlook. I always try and let all the private cars who are obviously following, keep together. They may be strangers to the area and not know their way.
I'd say it's OK on a dual carrigeway but keep it slow and relative i.e. if it's doing 20 don't blast past at 70, go 25 get in front a bit then respectfully speed up.
would never pass on single carriageway. would pass on a duel, but with respect.
there was a time i stopped on a roundabout to allow a hearse and the following cars to pass as one. it was safe for me to stop and i just didnt want to intrude on a familys grief.