While I agree that overtaking at 69mph in the outside lanes of major motorways is clearly within the law, I suspect doing so on any of the 120 or so miles of dual carriageway/ motorway (M5, M42, M40, M45, M1) that make up my daily commute you would incur the ire of 90% of people on the carriageway, not just the BMW drivers.
Personally I find myself equally irritated at people who use their (clearly ample reserves of) time to sit in the outside lane on motorways at or around 70 when there are perfectly usable lanes to their left but feel it's their duty, ordained by some higher power, to restrict me to a pre determined speed of their choosing
Being pedantic / standing on my high horse, if you are travelling within / at the speed limit, and clearly making progress on the vehicle being overtaken, why should any driver be pressured into either accelerating to pass the vehicle being overtaken quicker, and in doing so possibly exceed the speed limit, just to appease the following driver who wishes to drive at speeds breaking the limit?
I regularly tow a car transporter with my Omega, which is restricted to 60mph on motorways. I regularly encounter HGV's doing 1/2 mph overtakes in lane 2, which sometimes takes a good few minutes, and effectively partly blocks the motorway whilst doing so. I appreciate they officially restricted to 56 mph, but there actions regularly mean that I have to wait behind them for however long it takes them to pass another HGV as I cannot use the 'outside'lane (whether that be on a 3or 4 lane motorway). Imagine what their reaction would be if I flashed them to move over or get of the way - a V sign or other gesticulation would be the very least. Why should car drivers be treated differently just keeping to the speed limit?
I have a HGV Class 1, so I understand why it is done, but it doesn't mean it's right.
Going off at a slight tangent, another thing that irks me is motorcycles overtaking a line of stationary vehicles in the oncoming lane on the approach to traffic lights or junction and pulling in at the front of the cars. If I was to do that in a car and pull up at the front of the line of traffic before setting off when on green, holy hell would be let loose.
Rant over..