After getting nowhere with Honda UK, who completely denied that Honda made a replacement panel, I managed to source one from a company
www.carstereos4u.co.uk who offered a kit (panel and wiring lead) for £118 - it took a couple of weeks to get because they were on order from Japan and i was nervous about maybe getting some cheap third part piece of kit made from a plastic that didnt match!
I need not have worried when the well packed box arrived inside was a genuine honda accessory
P/N 08B00-SAA-5*0-A which came with all the possible parts you could need to fit a standard double din radio (or as I wanted a single din for which they included a useful pocket compartment to fill the gap)
Having read the 20 page genuine honda manual that came with it I decided to ask Halfords to fit it as they fitted my last one and have a standard radio fitting charge irrespective of how long the job will take.
I confess I am now saving my pennies to replace my nice Sony single din player with usb, blue tooth etc with a combined double din radio sat nav unit - now the panel is in place it should take no more than half an hour to fit a standard double din unit
I have written to Honda uK seeking an explanation as to why they could not supply this genuine Honda part - though with hindsight I probably got it cheaper than if they had!