I've read the replies as saying:
1. it was/is a pilot project.
2. seems to work - but not perfect (cost of in cab work)
3. good lessons learnt to pass on to future generations of technology (dives for Wikipedia for ATO▸ (Automatic Train Operation))
As for line speeds - my experience going westward was the Class 158/159s did a healthy 60-70mph.
Going eastbound - we did have a couple of lengthy (10-15min) pauses at passing loops - perhaps more typical of Single Line Operation that the signalling system.
As ever - thanks for all the informed help.