Thanks for the advice chaps but after a great deal of trial and error I seem to have cracked it. On paper it shouldn’t work but the following combination has done the trick.
HDMI from 4000T via HDMI to Scart converter box to EXT1 Scart socket on tv. RCA (red & white audio only) to corresponding RCA sockets EXT4 on tv. In tv setup menu, set “Digital input 1” to EXT4.
Bingo !
That said the damn thing has already dropped into standby for no reason twice already this evening, I fear I may become a regular on these pages 🙄
Best regards, Phil.