Eddie Wolstenholme and Mick Russell were both engineers and I'm sure that profession was well represented among the senior refereeing fraternity though I would imagine that teaching and the police service have probably produced the most senior referees followed by local government service.
Thinking back to those happy days when there used to be a referee pen picture in the programmes, I seem to recall that the most common occupation was sales representative, perhaps due to the flexibility of working hours.
Messrs Poll and Barber were sales reps for some of their careers. Messrs Styles and Knight ran their own businesses - that also helped with time off!