Ooh thanks Judith. That's the chap (George Nugent, and his brother was William Henry). You've answered one of my key questions in a rather different way! I was aware of his GWR surety from Charles Roper + John Tyrrell but always assumed that was his father John Tyrrell.

If that's Judge John Tyrrell, then that is likely because of JT's role as secretary of Mount Radford.

Thanks to your hint there I've found the other entry in the UK Railway Employment Records on Ancestry that refers to the Judge.

I still don't know why these children, born in London, were suddenly shipped off to school in Exeter, and whether there was any family connection. But I feel I'm moving somewhat forward - thank you!