I think there's nothing wrong with this from a highway code perspective, but it drives me up the wall as it feels like queue jumping!
Driving to work on the morning, I pull onto a 2 lane dual carriageway from a slip road. The traffic flows quickly, there are plenty of cars but it's not bumper to bumper. Traffic probably doing about 70 mph in the outside lane, 50 mph in the inside.
Quite often, as I join, there will be a car in the outside lane next to me. It will have moved over to allow those of us coming onto the dual carriageway to come on. Very kind. Obviously means I can't, at that precise moment, move out into the outside lane to overtake slower cars in front of me.
A car will be behind me, also joining. It will have been following me for quite some time,apmg another dual carriageway, round a roundabout, down the slip road. If it has no car next to it in the outside lane, as I have, it will often pull across both lanes of the dual carriageway in one go, and immediately be next to me, boxing me in from also joining the outside lane. I'm not going slower than it, I was ahead of it joining but am now boxed in by it as it won't let me out, and isn't interested in letting me out.
It all sounds so petty written down, but it's infuriating and winds me up everytime it happens.
AIBU to think this is bad etiquette.