Undertaking is dangerous. I despise it.
1) Having people overtaking on both sides is twice as hard to watch out for as if they only overtake on one side.
2) Visibilty is far worse on the wrong side. If you think mirrors cut it, you're wrong. Try driving a vehicle without any rear view other than side mirrors and see how many surprises you get from people appearing from nowhere on the nearside.
3) The Highway code specifies when it is OK to overtake on the inside and when it is not. It is well thought out. If you go against the rule then A) what you are doing is less likely to be expected - hence dangerous - and B) you have no justification for doing it.
4) People who overtake on the inside are reckless and impatient. Even if undertaking were inherently safe, those people make it unsafe.
Sorry, but undertaking is just another example of people doing whatever they like because they feel they should be exceptions to the rules. Another thing dragging down safety on the roads.
My rear view mirror can only see my passengers & nothing behind me. I only have my two side mirrors and there is no difference in what they can see. If I pick up a passenger on the wrong side of the road, my nearside mirror can see the whole width of the road to allow me to pull out. If I'm on the right side of the road, my offside mirror also sees the the whole width.
As I said earlier, we do not know if the guy was undertaking or had been in lane 1 for ages - and therefore simply passing on the left - which is perfectly legal.
If you are on a dual carriageway in lane 1 travelling at the legal speed limit & come across someone pootling along in lane 2 doing 5 or even 10mph less - do you..
A. Slow down & match their speed - thereby causing a rolling road block (which is illegal)
B. Pull into lane 2 & follow behind at the same speed they are doing (lane hogging is also illegal)
C. Carry on in lane 1 at the legal limit?
Alternatively (and I have been here more than once), I'm driving along in lane 1 maxed out on my limiter at 62mph, the road ahead is perfectly clear for a great distance.
I come across a lane hogger in lane 2 doing around 55mph.
I am not allowed into lane 3
Aside from my options (A,B,C above) what do you suggest I do?
The answer, and I have this from the guy in charge of motorway policing at Thames Valley Police, is to carry on at the same speed in lane 1.
What I did was not illegal & had the idiot decided to change lanes as I came past, HE would be at fault since you are supposed to use Mirror, Signal, maneuver.