Most of the bus companies were nationalized at the time and had the National Express chevrons logo next to the traditional name (Southdown, Mansfield District etc.). There was a 'Wanderbus' ticket (produced centrally for £2.40) which I think was just intended for unlimited day's travel on...
You've obviously never spent hours on buses!
I did a similar thing in the 1970s when I had much more time than money. I got from Worthing to Mansfield using nine local buses. Took me 16½ hours and cost about £2.60. I was absolutely knackered at the end of it, which is why I didn't return that way!