I just enjoyed a ride on this old bus between Quorn & Ruddington in Nottinghamshire but my bus-enthusiast friend tells me that rather than a standard Routemaster this bus RM121 is:

"...known as a 'Dartmaster', one of the buses that were refurbished by Marshalls of Cambridge for TfL a while back for route 13 and maybe some others. The engine is probably a four-cylinder something and not an AEC six with a new Allison auto-gearbox and not the four-speed original, and the winding windows have been replaced by hopper type".

(Quite a comfortable) HBM to everyone. Enjoy the start of the new week.