It's such a grey area, as said, surprised no-one's been able to quote directly from a highway code/similar book. It's a serious point, made, of course,and in the event of a collision - who is responsible - who's insurance pays for the damage/injury to who? Hmm...
Have to say I normally merrily bimble along on motorways in lane 1, and can sit behind a lorry, pop the cruise control on, knowing I'm at an economical speed, and will get to my destination eventually.

Hate middle lane owner's club (who doesnt?) but lane 3 has unofficially become the 'Exec Saloon / Porsche / Rep / Chav in Fiesta' lane where you can apparently do 90mph all day long without anyone batting an eyelid. The concept of a vehicle then overtaking said person in lane 2 seems to massively aggravate the lane 3 guy in the 5-series who has 'the right' to be doing 95mph, were it not for this 'idiot' 'crawling along' at a mere 70mph in some beat-up old Vauxhall Omega, getting in his way.
Off topic, but was in a 20 the other day. Car 6 inch off my back bumper. Now to be fair I was doing 22-25mph, so really I was speeding. But he was there, waving his arms, fuming mad at this 'idiot' in front of him. Sorry, but if you do the maths I'm basically doing 20% over the speed limit.

That intimidating attitude precipitates me to want to move to 30, and potentially get done for speeding... again. And it's ultimately that intimidating attitude that causes accidents.