The car mentioned earlier, HX6507, is coming up for sale at Bonhams: https://www.bonhams.com/auctions/22724/lot/106/
For info though, an account of the car appeared the Riley Register's Bulletin No.111, Sept 1983. It is said that during its history the WD spec 21" wheels were replaced by 19" wheels; the crown wheel & pinnion changed from 6.75 to 5.25 and then to 4.89 (from an RM 1.5 litre); twin carbs fitted; and the back end was hacked off to fit a Monaco-style boot. It looks as if the wheels and carbs haven't been re-instated but at least the body has been changed to what looks like the Mk IV style. But why wasn't it painted green? Sigh.
Hopefully the next owner will go the extra mile and return it to its original staff car look.
At least two other WD tourers exist - at least one of them rescued from Mr Passey's well known yard. For a picture of one of the cars, go the Riley Register's home page, click on the 2012 rally plate and go to image 13.
Personally, I think the estimate is too high - I've seen Mk IV tourers, which essentially is what it is, at the circa £15k mark. But the price of these things rarely go down!
If anyone is interested, I'll dig out some little known gen on these staff cars.