You are quite right Mocas, sorry when I re read my post I agree my use of terminology was quite poor
You are quite correct there is no "offence" of undertaking however in law there is an "act" of undertaking, which in the situation we are discussing would be a car travelling past the hogger car in lane 2 in lane 1 and then returning to lane 2. This is what magistates consider as the "act" of undertaking. It could obviously also apply to a car undertaking in lane 2 and then moving back to lane 3, or lane 3 into 4, you get the picture
That could be interpreted as saying that , in order to carry out the 'act' of undertaking , you would have to start off in a position of being in the same lane as the 'hogger' , then move over to the lane on the left , pass on the left and , finally , move back over to the right - effectively a 'mirror image' of a normal overtake .
It could , perhaps , be argued then , that a driver proceeding along lane 1 at a constant speed who happens to pass a slower vehicle in lane two , without ever moving into lane two , does not carry out the act of undertaking . Even a driver who joins a carriageway , entering lane 1 , and happens to pass a slower vehicle in lane 2 ( the slower vehicle may even have moved out to allow the driver to join from the slip road ) , subsequently moving into lane 2 to pass something slower in lane 1 , arguably has not completed this 'act' .
My own feelings are that those who fail to use lanes properly , and fail to keep left when they could make the same progress there , are most at fault since there would be no 'undertaking' possible if they kept to the left .
The majority of drivers who 'undertake' are simply trying to make reasonable and legal progress along a road , despite being obstructed by a slower driver who could , and should , move over to allow themselves to be overtaken .
I won't say that I never pass on the left , in some circumstances it is permissable , usually I will move from lane 1 to lane 3 and back to pass a lane two hogger , but I have seen me pass them on the left if exiting shortly ahead and it seems clear they are not ; I have also cruised along lane 1 of near deserted motorways past nitwits traveling in lane 3 at a lower speed with no reason to be there .
Here in Strathclyde I have observed traffic cops deal with lane two hoggers by coming up fast in lane 3 then 'swooping' across their bows towards lane 1 , it does strike me as not a little unsafe , effective as it sometimes might be .
I have at times felt like getting one of those dot matrix signs for my rear window , but I doubt that it could store enough messages for every situation ; nor might some of my thoughts be printable