Stinky.
The road tax expiration date in the ad doesn't match the date that the DVLA gives for the S8 with that plate.
If you google some of the text that's in the ad, amongst all the scraping sites that refer you back to this ad, you find a May 2014 autotrader ad. The page itself on AT has expired, but the cached version is still turning up in google's results. My guess is that the text has been copied and adjusted and it's a scam.
ETA: the last 3/4 of the text bears a remarkable resemblance to this ad:
http://www.decassoncars.com/flyer.php?id=5478 (for some ****box Honda).
We'll find out, as I've sent the "seller" a message!