if you are on the motorway, on far outside lane, someone is doing 60 infront, its illegal for you to go into the inside lane to undertake him, you seem to think this is illegal, i have heard of people getting a good bollocking for it and google says on tv traffic cops gave someone a nice prize for it, im sure if i looked further i would see people getting points for it.
No it isn't, of your driving with due care and undertaking properly I.E not speeding, lane hopping, then it's fine, your still confusing dangerous driving with undertaking, again i will say there is no law for undertaking you cannot be prosecuted for undertaking only what they deem as dangerous driving, but you can legally undertake provided you do it correctly, anyway i have said it enough times.