We
occasionally got Servis machines in our shop back in the late '80's. They also did some interesting things with ramping up the spin speed, using a spring-tensions pulley to vary the ratio, didn't they? I am not quite sure about that, tho - long time ago and didn't see too many.
That drum design worried my boss a lot, he felt they would do the same poor job with sand as the solid tub top loaders.
How did they do with sand? I can well believe that they would have produced comparable washing results otherwise with less water and thus less energy for heating...
Oh, and, welcome, by the way. Please don't limit yourself to only the UK postings - there are a lot of interesting vintage machines. Sometimes there are even new machines which are worth noticing, every 20 years or so...like the Dyson dual-drum.