A bit more R & D...
I found this pic on the 'net, so again, not my (c) and I could not find any attribution.
It's interesting for several reasons. First it's the only one I've seen from this point of view, and shows a great image of the china clay loader, tracks, hoppers and so on. Even better, whilst undated, if the ship tied up to the jetty is the 'Crandon' as marked on the pic, then we can date the photo fairly precisely, as being between 1927 and 1933. That's because she started life as the 'Gardenia' in 1914 on the Tyne and then was regularly sold on and renamed, in 1927 being sold to Crandon Shipping in Cardiff who renamed her 'Crandon' and then sold her in 1933 when she was again renamed 'David Dawson'.
See these links for details:
Also, as the links give the dimensions - she was 100m long - scaling the jetty etc becomes possible.
In terms of operation, the second marked up photo shows a line of trucks just about to be shunted one by one over the tippers at point 'A'. The wagons are end tippers and the clay falls under the tracks onto a conveyor belt which then lifts it up to the top of the loader, then a second short belt moves it onto a third belt which is parallel to the jetty edge. Finally, a movable short belt carries the clay up over the jetty side and into the vessel holds. Note that this belt can traverse almost the entire length of the jetty to reach any hold on a moored ship. All designed and built by the GWR!
If anyone else has any more information I'd love to hear about ti - thanks.