Got her out and had another spin in the sunshine. I am beginning to gel with her now, not as easily as the 650 single, but with new tyres this is going to be a lovely bike to go away on fishing trips with.
Its this -https://www.siebenrock.com/en/products/luggage/4654200.html . I got mine direct from Seibenrock about 5 years ago, but seems that you have to go through a "dealer" now. At some point they were also available from Motobins/Motoworks/James Sherlock but not sure nowadays....
So it should be for £200 for a small leather bag! i reckon if you showed the picture to any leather crafter they would make one equally as good for £50.