Oh dear. there are some very mis-informed drivers amongst us.
The highway code most certainly does NOT say it is ok to undertake ever! What it refers to is lanes of SLOW moving traffic and your lane moves a bit quicker, then maybe another lane moves a bit quicker. It does NOT imply or suggest that you change to a lane on the left to overtake - except in a one way street. Traffic moving at 50-60mph is not slow moving!
As for driving at night and you come up on someone going slower in lane 2, you MUST overtake in lane 3. It is only a matter of time before one of these drivers suddenly notices you at the last second and moves over to lane 1 to make room. then you will have a serious problem.
I agree that they can be annoying. If I am on the M1 and there are lorries doing 60mph in lane 1, I will sit in lane 2 at 70mph unless there are very long gaps between the lorries. This is because I do not want to have a car half overtake me, sit on my rear wing and thus force me to slow down just to pull out behind them to overtake another lorry! Also, as I am doing the maximum legal speed anyone wanting to go faster wants to break the law. I fail to see why I should end up being inconvenienced and forced to get boxed in just to help someone who wants to speed!
I am aware also that if I am in Lane 1 doing 70mph, I am often the slowest vehicle on the moroway and do get passed by just about everything, including Mercedes Sprinter vans! As a guess I would think that the majority of car drivers do about 85mph on the motorway.
As a PDI I do not have the desire to get endorsements. I need my license. I regard myself as an extremely good driver, but unlike most other drivers who think likeewise I have had my beliefs confirmed by the DSA who agree that I am an expert driver.
Don't get me wrong here guys. If some idiot in a BMW or Audi (usual culprits) wants to fly up behind me at 120mph, I am not staying where they may collide with me. I am able to get people to drop back safely or force them to overtake me without them even realising it. I do not get into gestures, sudden braking, hazard flashing or any of that stuff. I also have never had an accident in 26 years of driving!