Bit of trawling of the internet and I find Europartsdealer with a new replacement item at £7.79 with free 1st Class Delivery from Royal Mail.
Ordered it Late Sunday night, and the little brown cardboard box, with the mirror wrapped in bubble wrap, arrived today from Redruth in Cornwall.
...and less hassle for me than a 60 miles round trip to the nearest Halfords.
So three cheers for the internet, e-bay, europartsdealer, and the good old Royal Mail

Regards Neil