I rather embarrassingly found out decades ago that there is no offence of overtaking someone on the nearside (undertaking), I won't embellish, but those who know me can probably join the dots
Central lane hogging is actually a tad more serious than just mildly annoying. Around 40% of collisions occur in the right hand 'overtaking' or 'fast' lane as some call it. By hogging the central lane you are forcing most drivers to overtake using the right hand 'fast' lane where the greater majority of collisions occur, as most people believe you can't undertake, which you can. The road may have been empty for this driver, but it's a point of habit and drivers are creatures of it. If they do it when the roads are empty, they do it when it's full as well, so they need educating that's it's not best practice, potentially hazardous and an offence. Road policing units have been encouraged to enforce this for a number of years now, that's a Home Office directive, not a police officer having a bad day and looking for tickets! Collisions occur when drivers have to change course or alter speed and if you're hogging the central carriageway unnecessarily, it's a potential consequence and any collision on a major route is enormously expensive.
Any action where you cause another driver to unnecessarily change course or alter speed is careless or inconsiderate driving and punishable - it's quite simple really. Another great example is entering a motorway or road via a slip road. Those are give way lines as you enter, so you have to give way to the traffic on the main carriageway. Barrelling down and entering at speed causing anyone to change speed or alter course to
accommodate you is actually an offence as well.
If you drive in the far left lane you are nearly twice as unlikely to be involved in a collision/incident as when driving in the far right or outside lane. Additionally, if something does happen you often have an escape area to head for to your nearside, in the other two lanes you've got nowhere to go except into other traffic, especially if it's busy.
We've still got pretty safe roads though, just check out some Russian dashcam footage if you don't believe me