Excellent!!! I was just reading another persons similar problem and was trying to track it down. Many thanks for that. It does indeed now compile and MPLAB IDE lets me upload the code to the PIC.

Out of interest, is there any way that I can check if the thing has actually switched to the external oscillator [short of removing the oscillator!] by looking at the assembler file?

Many thanks all for help with this - has been bugging me for hours!