The police should be concentrating on those in the right hand lane that should be in the left

Undertaking would be a non-issue if proper lane discipline was followed. Solve the lane discipline problem and you will stop undertaking as well.

People that dont pull left on motorways and hog the overtaking lane are the oneswho should be pulled over and fined .

"...the middle lane or the overtaking lane...". The middle lane IS an overtaking lane.

one of my pet peeves is when I've just completed an overtake of a fully loaded HGV, still in the middle lane, looking to take the left lane and some berk in an Audi undertakes me doing 90. Always an Audi.

The big problem with this rule and interpretation is that if you are driving in the left lane and someone overtakes you in the middle lane and slows down, you are then obliged to also slow down. If you are driving steadily (esp with cruise control), this is very annoying and sometimes hard to avoid. I would also note that flashing your headlights to move someone out the way can be interpreted as aggressive behaviour and the police will likely stop you for it if they see it.

If you had moved over to an empty looking inside lane that van driver would not have to go past you on the inside.

This guy knows what he's talking about and is giving free advice.
I drove HGV's for over 32 years and didn't know this.
I've learnt something new today and will be a better driver for it.

A good rule-of-thumb when confronted with 'issues' on the road is to ask yourself,  "What would I do if the vehicle behind me was a Police Car?"  In most cases, you'll find that you KNOW what is the correct course of action.

How slow is traffic before it's a queue? If you can't give an answer then it's subjective and will be debated.

Yes, lets slow down EVERYONE behind me doing 60 because some muppet doing 50 on the right wont move over

While travelling along the M40 I came across a vehicle in the middle land.  I then moved from the left hand lane all the way across to the right hand lane, passed the vehicle then moved all the way back to the left hand lane.  Shortly after that I then did the same again for another middle lane crawler.  Then after doing this a third time the police (who had been following me the whole time and not once used the left hand lane) pulled me over.

They argued that MY actions constituted incorrect use of the lanes.  I asked them why they hadn't pulled over any of those centre lane crawlers and why they themselves hadn't used the left hand lane once, while they were behind me.  They let me go without issuing any ticket but still did nothing about the centre lane crawlers.  I continued my journey hogging the centre lane like everyone else, using the right hand lane to overtake. (since the police were still behind me).

It's not just that the police won't enforce the law.  They actively expect everyone to conform to the normality of breaking it along with everyone else.

It has always been illegal to lane hog - so if the police enforced this law, the lane hogs would soon stop doing it.

Best, and most relevant comment I've heard in a very long time - 'It's not our job to police the roads'. Absolute gem!

Middle lane hoggers who overtake nothing,  and also speed up when you try to overtake on the right.

On the M25 recently the 2 outer lanes were traveling at 45-55 mph as it was very busy and there was lots of braking.
The inner 2 lanes were virtually empty, the occasional HGV every mile or so, and a few cars and van in lane 2.

Lane 1 of the 4 Lane sections of the M25 is often empty whilst lanes 3 and 4 are full of tailgating idiots going slower than i am. Its far safer in these scenarios to stay in lane 1 even if you are going faster than them and effectively undertaking.

With only 2 cars on the motorway Its rediculious to say the car in lane 1 cannot undertake the one that's hogging lane 4.

I note the HW code doesn't actually state or define 'Slow Moving Traffic'.  A queue can form in the middle lane at 40mph on the motorway...  I don't overtake on the left, but the code could be updated to clarify.

The takeaway here is: when rules are stupid and contradictory, people will justify ignoring them.