At about the time of "British Coachways" I remember the "City-Flyer" services from Blackpool to Dover, run by a consortium of Burnley & Pendle, Leicester Corporation Transport and Maidstone & District. I think the brains behind the marathon route was Geoffrey Hilditch, who'd been GM at Halifax and then at Leicester.
I seem to remember it ran three times per day, but with one "short-working" which terminated at Maidstone!
Starting at Blackpool, it was non-stop to Blackburn [I don't think it was allowed into Preston Bus Station], then Accrington, Burnley, Halifax, Sheffield, Leicester Charles St.[diverting off the A50 to serve Beaumont Leys], London Gloucester Rd, London Aldgate & Maidstone to Dover Docks.
I doubt many people travelled throughout[except coach enthusiasts], but it seemed to be well-used for certain sections of the route, e.g. it was well-timed to allow a day-return from Halifax, Burnley and Accrington to Blackpool.
I was working in Leicestershire at the time, and my parents who lived in Halifax used it on several occasions when they visited, for it allowed far quicker journeys than National Express, and direct too.
I had a ride on it once, from Beaumont Leys to Dover, and was amazed the fare was only about £6 return.
Unfortunately, punctuality was a problem with such a long route, and the service didn't last very long.
But, interesting times in the coaching scene.