Does any body know whether D qualifies? The website only mentions J (ok) and z (not ok). (In PE it only seems to be the K fares that don't qualify - W & S do) As GoldenOldie points out, it is almost always going to be cheaper to buy 2 X Z than 1 J to utilise the companion ticket. Remembering also that taxes, etc have to be paid for the "free" flight as well. As an example, I've just paid £1370 each for Z fares - the J fare was over £4,000. D (I think), was about £2050 - this was the fare that appeared when all Z availability had gone.
I'm really interested as I've converted to a Virgin credit card (fee paying) and will easily post the required £15K spend for a companion flight.