I think I have fixed it.
I cleared all Arduino 'stuff' off my PC, except my sketches. I also cleared references to Arduino ERW 1.03 from my system path.
So with a virtually Arduino IDE free system I installed V1.6.5 and then ESP8266 support as per previous post.
The sketch now compiles without the 'F' was not declared in this scope error.
Thanks for your input.
Regards
BillP