I've been driving poorly recently, but am I wrong about this

[Animal]

Apologies in advance, because I'm sure there have already been several threads about this, but I've noticed more and more frequently in the past couple of years that the general population seems to treat motorways as if they're French autoroutes (i.e. stick to the two lanes on the right).

I've stuck to doing what I always do, which is to keep left unless overtaking and try and roughly maintain 70-ish - even if this means I'm passing cars on my right (them being in the "overtaking lanes" at 60-65mph) Does this count as undertaking? Should I slow to match their speed even if my lane is clear? Would I be justified in ramming them out of the way?

I thought I'd seek some guidance because I had a bit of aggro with another driver on the motorway at the weekend: he didn't like that I'd passed him and so decided to follow me, changing lanes behind me, matching my speed, flashing me and waving his arms around in some kind of moron semaphore. Said driver swerved to pull alongside me and I slowed to find out what the problem was (for all I knew I had something hanging off the back of my car etc) at which point said person starts waving a camcorder at me, implying that he has my transgressions on camera! Ignoring the fact that he's arguably earned some points and a fine for doing so, I eventually just slowed down to the point where he got bored and drove off.

I'm not arguing that I'm innocent ans was driving well, nor that I rose to the bait, but it's made me think about the quality of my driving, which is something that I've always been keen to uphold. Evidently there's room for improvement...