I have some Jag ashtrays.......funny about that, seeing as I have a Jag.
When I can be arsed, I'll check and see if they fit.
I don't recall if the XJS and my S3 XJ6 use the same ashtray, but seeing as Jag used the same design on S2s and S1s I'd be surprised if they'd go to the trouble of designing and making something different for the XJS
"Keep calm, relax, focus on the problem & PULL THE BLOODY TRIGGER"