When I first set the system up there was some "juddering" when I tried to use 24-frame mode. Pressing the Info button on the telly showed a 1080p60 signal being received.
I fiddled with the AVR settings and set the HDMI mode to "bypass". The TV's status changed to 1080p24 and all was fine.
When I had some more time to play around I discovered a "frame rate" option on the Arcam's setup menu, 50Hz, 60Hz, or As Source. However I've left it on bypass. My Denon BD player outputs a 1080 signal regardless of the source (upscaling if needed). The Freesat+ box upscales SD to 1080p and deinterlaces 1080i to 1080p. So the HDMI upscaling isn't needed in the AVR.
I only have two video sources (BD and Freesat+) and the TV's internal Freeview HD tuner. No need for up-conversion from composite etc.