There seems to be a general electrical failure ( circuit short to battery or open) , the mirror does not clear the frost at all, whereas the drivers door one does pretty quickly

GAP IID error B1163-15 (2F) Left Mirror Heater Output

Has anyone had a similar fault, not the end of the world but annoying first thing in the morning

Is it just simply a corroded wire or maybe disconnected along the wire path, which would mean changing the mirror would not solve the problem ( unless it is internal wiring inside the mirror which fails) - any heads up on the fault welcome please

A first step could be to pop the mirror glass out of the housing, and see what the condition is, that way you could check the condition of the wiring connection and heating element. It always seems to be the nearside mirror that suffers corrosion due to puddles / dirt etc against the kerb. Once popped out you could use a meter to check the connections.
You could pop out both glass sections and swop ( Just connect wiring, not fit in place obviously ) to check if the fault is with the glass or wiring feed.

confirmed, I took both heated door mirror glass off, then ran IID Faults again

Click image to enlarge

That is a good result, no messing around with wiring, and a cheap fix, decent quality replacements are about the £20 mark