Apologies for the late reply.

@tumbleweed
your mods got it working, many thanks for your advice.

@Richard
no joy using the ASM approach - the led locks up in the condition it was at the moment of button push and no Int! seen.
Removing INTCON and/or PIE0 (as with tumbleweed info) stops any interrupt happening so the led blinks away. If you want I can send
a couple of 16F18426 for you to test Richard. Let me know please.

Cheers,
Bill