There's a strong argument that continously changing lanes is the most dangerous part of motorway driving. People who go from 1, to 2, to 3, overtake at 90+mph and then cut across from 3, to 2, to 1, and off the motorway in front of traffic are FAR more dangerous than if they just undertook a vehicle and left the motorway. Similarly, people who sit in the middle lane may well be doing so because of the fact that lane 1 can be heavily rutted by lorries, and to ensure they're not constantly changing lanes every time a slip road comes along - they've left you perfectly enough room to overtake, and as long as they're not crawling at 40-60mph it's not really an issue.