Two things about Viscount wheels, one is that the driveside toothed locknut is usually made of brass, which is very slippery and predictably causes the wheel to shift in the dropouts. Threading is standard so normal steel locknuts can be easily substituted.

Secondly, the Birmalux clincher rims I've seen on some Viscounts seem to have been rolled into a hoop using a hand-cranked rolling machine, such that the variation in the cranking speed leaves the rims lumpy, i.e. not very round.