I spoke to a nice man on gumtree selling a 531 trent valley badged bike.
He said he spoke to the part owner; the company was run by 2 brothers, one was the builder and the other was the salesman producing from late 60s to 70s from what i remember him saying. They produced bikes until they fell out for some reason and the builder brother did frame building at a different company. I spoke to the cycle inn shop in nottingham they said the company made a couple of bikes, seemed good quality.