Back to the OP….
I've no idea how anyone managed to cast judgement on this as we don't have enough info. I'm assuming the 400yds mentioned is 400yds between the two lorries. The key bit of info required and missing is the closing speed. If you were only doing 1mph more than the 2nd lorry that 400yds could take (quick bit of maths) 15mins – if your closing speed was 30mph then it's 30secs.
No idea what the "rules" are on these things but I'd call it a single overtaking manoeuvre and stay out if there was about 20secs between vehicles overtakes, a bit less on a busy road, a bit more on a quiet one. Other factors to effect my judgement call would be if there was another lane free to my right, if there was someone closing fast behind, if there was someone who had been closing fast behind but was now waiting behind me and I could release and the likelihood that moving in left would get me boxed in. Without being there, exactly what is best is impossible to judge. Also one man's 400yds is another's 200 eh chaps!
I have been annoyed by middle laners in the past and (not proud to say) have been known to show it by moving swiftly from the fast to the slow once (just safely) past them. I never get annoyed if you can see what they are doing though, i.e. making a very long overtake, even if it's not exactly how I would act. No stats one way or another but I would imagine a lot of accidents on motorways are centred around one car lane changing so all of us doing more than necessary is probably not a good thing. The only middle laners that actually annoy me are those that do so on nearly empty roads with the next car in the left hand lane ages away or actaully travelling faster than the middle laner.