So few people seem to understand merge in turn.
With regards to people driving in the middle lane, if the motorway is empty apart from a car in the middle lane, and I'm catching up in the first lane, can I go past without moving out?
I was having a chat with a traffic copper about this one a few years back (no I hadn't been pulled over, I have a few police customers)
Apparently he'd taken a case to court for someone doing that and lost (magistrates court, so non-binding) the magistrate told him that if you can move over to the left without cutting someone up, go past at a normal 70 mph and move out without getting dangerously close to a vehicle in front and without cutting up the MLM then the manoeuvre is safe and the correct cause of action is for the copper to pull over the MLM and do them for driving without due care and attention.
In your case you aren't even changing lanes to go past the MLM. I know the exact situation you mean, encounter it from time to time when night driving. I just stay in the lane and carry on as if they wern't there.
For a fun game, try to time it with someone who is overtaking them in L3 at the same time, and aim it so that you both appear in the MLM's field of vision at the same time. That usually wakes them up and makes them move into L1.



