I noticed that someone arrived on this site this morning having searched for "the model for Davey Warbeck". I don't know whether they found what they were looking for, but the answer is Eddy Sackville-West (a cousin of Vita's). Davey is, of course, a memorable character from Nancy Mitford's novels, first appearing in The Pursuit of Love where as husband of Fanny's Aunt Emily, he becomes a favourite with the family, even the irascible Uncle Matthew:
" 'Pig's thinkers, Davey?' Uncle Matthew lifted the lid of a hot dish.
'Oh, yes please, Matthew, if you mean brains. So digestible.' "
I love Davey, who was brilliantly played by Michael Williams in the 1980 television version (Love in a Cold Climate - the price of that DVD is another reason to sign up to Lovefilm), and he and Lord Merlin, who was based on Lord Berners, are an excellent double act. Eddy Sackville-West cropped up in my reading earlier this year in Inheritance: The Story of Knole and the Sackvilles by Robert Sackville-West (post on it, including the sought reference to Davey W., here), but the man prone to bouts of ill health and hypochondria is very warmly portrayed by Nancy Mitford as a good egg, and someone to whom one can turn in a crisis, albeit with affectionate leg-pulls such as this one about Louisa's wedding:
"Everything had gone like clockwork, and there was only one small incident. Davey slipped out of the family pew almost unobserved, in the middle of 'As pants the hart' (Louisa's favourite hymn), and went straight to London, making one of the wedding cars take him to Merlinford station. That evening he telephoned to say that he had twisted his tonsil, singing, and had thought it better to go immediately to Sir Andrew Macpherson, the nose, throat and ear man, who was keeping him in bed for a week. The most extraordinary accidents always seemed to overtake poor Davey."
Time for a re-read, I think, as this is one of my very favourite novels of all, and Davey a lovely character. Perhaps you have an 'Uncle Davey' of your own, a fictional person you're particularly fond of; in addition to Captain Warbeck, I'll nominate Atticus Finch, a man measured on an altogether different rule - but how about you?