Yes Fran I agree that the 201's were really the first complete class of diesels to be named but I am more interested in why the likes of the older diesels like the A/C class and Sulzer/121/141/181/071 never received the same treatment.
As for a UKcentric thing when you look back at the history of Irish railways and see that it they originally came from UK companies building a major trading route to the British empires 2nd city at the time (Dublin) I surprised the practice of naming locos never really took on this side of the Irish sea. It would be interesting to see if the rest of the British colonies kept up this practice.