Legal to undertake on motorways and dual carriageways
If there's enough room tO undertake there's enough room for the inattentive fits to move over
Your wish is my command, it is perfectly legal to pass someone on the left on a dual carriage way or motorway.
You stay in your lane, at the speed you are doing, and just go past.
What you dont do is roar up behind them, swing to the left, boot it then as soon as you are past swing back out to the right.
You just plan ahead, set your speed, and get on with it.