How are there so many fast HGV's in the UK?

I have been noticing more and more fast HGVs on the road, doing just over 60 steady and 65 down the hills, according to my GPS. Overtaking at a "real" 70 feels very slow.

UK plates, not downhill, usually trailer units pulling curtain sides trailer, not a large company, some kind of shipping/delivery firm or building trade.

I thought they were all on a tacho and regulated to 56 ?