The way I see it, if I'm in lane 1 and cruise past slower moving traffic in lanes 2 and/or 3 without then moving into lane 2, then I'm not 'overtaking', it's just that they are in a slower traffic stream.
The number of times you see lane 1 empty with 2 & 3 with heavy traffic is depressingly common.
Through family commitments, I have become a regular user of the M25 on Saturday mornings and evenings. I have noticed the same behaviour but perhaps more noticeable because there aren't as many lorries in the nearside lanes. I have regularly been in lane 1 in four lane sections with lane 2 empty, lane 3 with only a few cars in and lane 4 being the busiest with occasional bunching. I don't like the idea of crossing three lanes to overtake the sometimes slower moving traffic in the busier outer lanes so prefer to maintain speed, stay in the same quiet lane and, yes, technically, undertake.
I recall an incident on the MI in the early 60s related to this theme when a well known celebrity (I think it was Tommy Steel) was prosecuted and publicly reprimanded through the media when undertaking in his e-type. I have regarded it as a cardinal sin ever since!
