My response would vary widely depending on the mood I was in at the time combined with my perception of what the consequences might be if observed by, say, a traffic officer or monitoring camera.
I'm going to assume that the vehicles shown are all travelling at between 50-65mph for no better reason than that is the most common circumstance I actually encounter, particularly on the London bound M20 on the way home from a continental excursion where, with the notable exception of Belgium, I am used to road users largely doing what they're supposed to. Let's assume that that is indeed the north-westbound carriageway of the M20, late afternoon (sun's over there). As you can see, the conditions are all good: visibility, road surface (apart from it being concrete), dry, warm, etc. Let's also make the entirely reasonable assumption that there are no qualified enforcers (HATOs, TOs, etc) anywhere in the vicinity (this is 2020s, not 1980s)
Mood 1 - ffs, why can't any of these dickheads do what even French peasants can manage in their 2CVs?
Ride aggressively, with of course my usual standards of observation and caution, up lane 3, high beams and spots on until 2 seconds behind rear offender then wiggle from side to side while flashing high beams until he finally notices and moves over. If he fails to move over before my patience is exhausted, move to far left of lane 2, move swiftly past then return to lane 3, 1-1.5 seconds in front of him, sit there for 15-20 seconds before doing something similar with the red cars if they haven't already taken the hint.
Mood 2 - (as mood 1 but) can't be arsed with these dickheads, let's just get home.
70mph on the satnav up lane 1, moving to far left of L1 to undercut black car in L2. It looks like the trailer is moving from L2 to L1, being slower than the white car who's probably out of the way by now, so move to L2 behind white car then L3. If the speeds were a bit lower, say, 40-50, I might well decide to filter between L2/L3 instead.
I have in the past sought advice on the legality of the L1 undertake and the consensus, including several TOs, falls short of declaring it to be legal but, assuming that I'm well-behaved, wouldn't result in me incurring penalties or even words of advice.
My direct experience of middle-lane hogs in particular is that they are simply unaware of the error of their ways or the inconvenience it causes to others. They do it on empty motorways just as often as crashingly busy ones. It's an education issue mostly although there can also be an element of laziness and/or lack of observation going on as well.
The issues involved in this artificial scenario are not black and white; there is no single "correct" response, instead the best any of us can do is to expose our thinking. It's almost like what we'd actually be doing if we were riding up a motorway!
ps. TO = Traffic Officer (Police, not HATO=Highways Agency Traffic Officer)