Every driver has their own story on driving and outside laner's and bad drivers.
The UK Law States in section 137:
On a two-lane dual carriageway you should stay in the left-hand lane. Use the right-hand lane for overtaking or turning right. After overtaking, move back to the left-hand lane when it is safe to do so.
For people stating that the law tells us to stay in the middle lane I am afraid they have or miss-interpreted it:
Section 134:
You should follow the signs and road markings and get into the lane as directed. In congested road conditions do not change lanes unnecessarily. Merging in turn is recommended but only if safe and appropriate when vehicles are travelling at a very low speed, e.g. when approaching road works or a road traffic incident. It is not recommended at high speed.
Please note the use of the word CONGESTED.
Motorway Driving Section 138:
On a three-lane dual carriageway, you may use the middle lane or the right-hand lane to overtake but return to the middle and then the left-hand lane when it is safe.
I hope this makes better sense of the discussion.
In my own personal experience my father was a Sales Director when I was a child, clocking up thousands upon thousands of miles often with me by his side. He was very vigilant about motorway driving, etiquette and dangers. Passing your driving test does NOT make you a competent driver, you are learning. You cannot switch off and sit in the incorrect lane. You will probably hurt or even kill somebody else and you will be totally unaware in your own little world.
The motorway is a dangerous place and should be driven with extra care, looking much further than the immediate car in front of you and watch your mirrors at all times. you should not make any rash dangerous manoeuvres but when safe you pull into the left and when you need to pull out you use your mirrors again, when there is a space then you indicate, then pull out, then you move back to the left.
If you are unable to understand this you need to be re-trained. There is a total lack of training for motorway and Dual carriageway driving. I have seen many Learner cars (instructors) driving with this annoying and very dangerous habit.
This is the Law, it is there for a reason, if you do not abide you will encourage road rage and could end up the main contribute to an horrific accident.