I found this one amongst some of my old photos. I can't see from the photograph what make or model this bus is, but I'm pretty sure that it is a Leyland RT. Put us right if you know differently. I can see that it is a number 302 from Hemel Hempstead to Watford.

In the fifties and sixties, books on bus numbers and how to idnetify buses were published. Mainly, they contained lists of bus numbers makes and models and children would spend hours at bus garages and stops just spotting them.