When speed goes up and down without reason and driver seem to be just passenger, that is what makes me bit angry, should be penalized activity, imo.
Also that is annoying when some lunatics join to main road from smaller road so that I need to hit brakes as they first turn ahead of me maybe less than 100 meters and then they accelerate so damn slowly, they drive maybe 5km same direction, usually less and then they turn away from main road and there would been several kilometers empty road behind and before me.
Then one pretty annoying type is this that drives 90kph no matter what speed limit says, when it is 100kph they are too slow and when there is 80kph limit they overtake and are again front of me, if there is short 60kph limit they just blast away doing 90kph. Is it really too hard for them to keep eyes open and pay attention to speed limits?!
It is no problem if they would drive 110kph when there is 100kph limit, but no, it is same speed all time.
In a city this type seem to be driving 20kph over limits and when city limits ends they reach that 90kph maybe in 5km distance, what?! moped engines in their cars? Well, these are just typical passengers at driver seat, they don't understand what means proper speed to certain situation, no they are very passive and very dangerous drivers, they will have accidents and afterwards they can't explane why, they are blaiming road etc. but the truth is they were not driving their vehicles!
Ok, I get sometimes angry at traffic, but I have learned to sit back and look morons make morons from themself, not my problem, I leave good space to them as when moose jumps to road they will not understand what happened, but I can stop on time before hitting anything or then I'm overtaken them and already at home
I think that we do have only 2-lanes to one direction motorways here, at least I have not driven anykind other

Well, when I'm driving I'm usually going past some city, for example Kuopio (Bit over 120 000 residents, considered large city), there I usually take left lane (overtaking) and I don't see usually anyone faster, but several slower cars, typically speed limit is 100kph, some places 120kph and other cars seem to be driving 100-70kph, some of them seem to have difficulties to maintain their speed, maybe too small engines?
I think that if you guys from London area would visit here, you would ask where everyone are when we have rush hours

For example, I drove once around 80km trip nearby here and I saw maybe 30 cars and this is not yet most quiet area, but maybe quite average
During daytime you can see from here my area traffic, I live near that city of Varkaus (free translation = Theft, funny name)
http://www.tiehallinto.fi/alk/kelikamer ... rat_3.html
Do you have similar cameras/service in UK?
Here from left you can click map to choose what area you like to look, then it opens camera photos when you click one of those blue camera symbols
http://www.tiehallinto.fi/alk/frames/ke ... frame.html