Hi John, tried to follow your instruction but I feel I don't have the confidence to continue. I booked an appointment with the local Apple shop and had the guy at the Genius Bar check it over. He did the checks you recommend and memory and hardware looked Ok. He did find some permissions incorrectly set, he thought these were stopping the boot. These permissions seemed mainly to be printer operating programmes that are pre loaded in the OS for plug and play service.
These were automatically corrected and the mac rebooted without further work. This took about 30 minutes and there was no charge so all's well that ends well.
Thank you so much for your assistance
Neil