I don't use Motorways very much - I find them boring, and other drivers bring out an aggressive side of me that I don't like. However, when needs must I drive in Lane 1. If I meet a slower moving vehicle in Lane 1, I pull into Lane 2 to overtake and then straight back into Lane 1..
Unfortunately, this does mean on numerous occasions I undertake some numbskull bimbling along in Lane 2.
I appreciate that two wrongs do no make a right, but the alternatives are either swinging across two or three lanes to perform an overtake or driving behind them with horn and full beams blaring, forcing the car onto the hard shoulder, pulling them out through the window and punching them to death.
I do exactly the same. If I am doing say 65mph in L1 and go past someone who is doing 60mph in L2 then I don't consider it to be undertaking as I have not made a manoeuvre, I am just continuing to do what I have been doing. I do, however, make sure the hard shoulder is clear when I pass them and keep a close eye on their road position.