Wiki says:
"Cooper has acknowledged that the character of Campbell-Black was inspired by David Somerset, 11th Duke of Beaufort, Andrew Parker Bowles, the former husband of Queen Camilla, and Michael Howard, 21st Earl of Suffolk"
I remember reading the interview where she said it. None of them really stand up to the "Rupert hype" looks-wise (I mean, who could?), so maybe it's a meld of their personalities...?!
I think APB used to be quite the "ladies' man" in his youth.
70isaLimitNotaTarget
The "name" books (Emily/Harriet etc) originallly had photos of Jilly made up to look like the title . Years ago ( late 80s) my DH bought them all for me
Very jealous, 70iaLNaT 
I used to have the full Jilly set too but lost them in a house move.
The new ones haven't the same feel but are definitely better than nothing.
At least they haven't been made more acceptable for the 21st century yet, afaict.
They can be very samey with the same phrases repeared
Oh, dear me, yes: people always "rock up" in their cars; someone being sick always "throws up and up and up"; the nouveaux riches always say things "May hubby and Ay" and have "serried ranks" of clashing bright flowers and as for Pearl and her "boxer dad" in "Wicked", in case we couldn't remember from one page to the next...
And why is Taggie always "shifting shyly from one leg to another"? It sounds like she's desperate for a pee.
Obviously hasn't put me off, mind - I appreciate I'm totally over-invested 