No one are really buying diesels over 20k as they believe they will be hit with higher tax's and diesel prices in the future. A car dealer friend said the diesel market is dire for cars that has the potential to lose a shed load of money. He said anything under 10k is still shifting as the risk is lower. He said px prices he offers for diesels has reduced massively in the last year.
These still have a long way to fall. It's lost a little over half its cost in 4 years. But it'll end up in single figures like all 4 door diesel barges. You can buy a QP V for Â£10k, and that looks better and has a Ferrari built petrol V8 to hold up its appeal. The QP VI isn't as special so in theory it's low point will be even lower than that of the previous model.
I'd guess that this particular car is likely to depreciate at around Â£300 to Â£400 a month for the next couple of years at least. And then at maybe Â£200 a month for the couple after that. Giving it a value in the low teens in 4 years time.