For the history-lovers-- according to the "Making of Aristocrats" feature included on the DVD, as much clothing and jewelry as possible was reconstructed from family portraits (and other paintings from the era), as were wigs and other headwear; the costumers, hairdressers, etc., spend some time discussing their recreations (and explaining their reasons for the occasional deliberate inaccuracy, such as the wearing of black for mourning). Actress Sian Phillips points out that with one outfit she is wearing a antique lace fichu from that period, so it's probably safe to assume that other vintage items also found their way on camera.
And favourite giggle moment ... sisters Caroline and Emily in private conversation the day after Emily's wedding (Caroline has been married for seven years):
Emily: Is not the act of love ... strange? Jimmy says that its frequent use is necessary to a woman's health and happiness.
Caroline: That's abominably indelicate.
Emily: ***laughs*** He says what he thinks.
Caroline: I'm sure one sees many mighty comfortable old virgins.
Emily: Perhaps that is so. But one is awfully glad to not be among them.
Caroline: ***bursts into laughter***