Lots of lovely advice, thank you everyone. Never even heard of orange essence cassa, although I have been putting dried orange peel in my pots in the garden to stop him pooing in them rather than in his litter tray. Sigh.
I have one of these posts for him Hopkirk, so probably what you describe. I had one the same for my other two cats and they were fine with it but I gave it to a rescue when the last one died:
http://ecx.images-amazon.com/images/I/81X2-piGHwL._SL1500_.jpg
I think I might move it to the bedroom where he scratches the carpet and buy a flat one to lay there as well. I don't have any left over bits of carpet and I'm certainly not cutting a hole in the bedroom one even for him. Oh and woofgang, you are probably right.
Prudie he does scratch the mat outside of the patio doors so that might work. I'll see how I go with the less unsightly things first as I'm more than likely to trip over a door mat in my bedroom doorway especially in the middle of the night.
Thank you, all of you, for your invaluable advice. I hope he takes it.