50mph zones and trucks for tailgaiting/speeding can be bad, as some leave the cruise at 56mph as they reckon they won't get done. See it alot in te average speed cameras on the m25 and round the north circular. On the motorways it always seems to be te Irish or foreigners (not trying to stereotype here) toeing it to Dover for the ferry and on the north circ and a13 seems to be the tipper driver mob who seem to want to be everywhere yesterday.
There's a percentage of every vehicle type on the road that give them a bad name, can say similar stuff for bikes, 4x4, prestige motors, trucks, coaches etc all have their bunch of idiots who shouldn't have been given a license and ones who drive as you should.
But back on topic, as for lorry's overtaking on dual carriageways I bet any money the truck being overtaken is a supermarket truck as by law they have to go at least 10mph under the speed limit to get their hours in