Oh, and cahn, one more Mitford detour: it's one of the theories in Harry Potter fandom I'm utterly ready to believe that JKR modelled the Black Sisters on the Mitfords, as in:

Andromeda - Decca
Bellatrix - Unity
Narcissa - Diana (co-starring Lucius Malfoy as Mosley)

No Nancy equivalent in the House of Black, though.