Pity the traffic police dont agree with your view, and you can get done for it.
Actually, traffic police won't. I've had occasion to drive along the motorway in a minibus, limited to 62mph. On 2 occasions, I happened across a car dawdling along in lane 2. Given that my top speed was 62mph and I could catch them up and overtake on the left, their speed was well below, probably around 50mph.
Since I wasn't allowed in lane 3, what was I supposed to do? The law is quite clear on what I'm not allowed to do - not allowed in lane 3 & not allowed to pull out behind the lane hog and intimidate him into pulling over.
So I simply drove on by in lane 1.
Funnily enough, on both occasions, the idiot in lane 2 decided to report me to plod - well, easy to do since the company name and number was [plastered all over the vehicle.
On both occasions I had plod paying me a visit at work. Fortunately, I always drive with a dashcam and I always save any footage where my driving might be called into question.
So, knowing plod would be calling back, I dropped the relevant files onto a thumb drive for plod to view on our computer at work. The cam records in 3 minute sections and I made sure to get plenty of the before sections so plod could see just how long I was in lane 1 for - and just how empty lane 1 was.
On both occasions, plod agreed with my actions (driving by in lane 1, keeping my speed steady all the way) and said that they would be having strong words with the idiots that had reported me.
Had those traffic police decided I had done wrong I could've easily defended my actions in court.
How stupid would it be for me to drop my speed to match the idiot in lane 2, thereby creating a rolling road block, forcing everything coming up behind at 70 to throw out the anchors and try to get into lane 3 as well as creating miles of tailbacks from all the vehicles not allowed into lane 3
BTW, plod also said to me that "undertaking generally involves a wooden box, a long black vehicle and several people crying" whereas overtaking on the left is moving out from behind the vehicle in lane 2, passing them in lane 1 and moving back out into lane 2, the opposite of a normal overtake.