I got my programmer to work. It is the David Tait classic printer port programmer. I am using an ATX computer power supply which is common ground for 5V & 12V.
Both voltages are switched by the programmer using small PNP switching transistors. These are then inverted in the software setup to supply VDD & VPP.
Probably because of the common ground, I found by trial & error that I had to move the 2X series diodes from PS ground to PS 12V. I am not sure that these are needed in my setup, but it works so no changes for now.

I have done about 8 program runs and had no failures.
Last program was a "LED walk" from PORTC-0 to PORTC-6 which I adapted from a PORTC-0 flash asm program.
It programmed first time fine. Only worked from second time due to code bug. For some reason the BTFSC & BTFSS commands works inversely to my logic!