Searching for the title and author of a novel.  I read this book
in the early to mid-1990s.  Written in the first person perspective -male, British.

The narrator is a sociopath who is obsessed with (in love with) his older
cousin? half sister? Veronica? Victoria? -and destroys her.  She ends
up in a nursing home? insane asylum? dead from suicide?

Much of it takes place during the narrator's youth which was spent in
some sort of boarding school during WWII.  I think it was basically a
set up as a country-side refuge for children to escape the bombing of
London.  He was extremely devious and successfully executed some sort
of complicated plot. Might have involved his cousin? half-sister's?
broken leg.

As an adult, he gains political power as a cabinet? parliament member.
 Claims to have coined a term like "sexual politics."

I (mis)remember the title as something like: "V is for Veronica?
Victoria? Victory?" and the author as a "David Choate."  My attempts
at seaching based on these things has been futile.

Wow, this was a tough one!

It seems that the author's last name was "Caute" rather than "Choate."

The book was "Veronica: or The Two Nations" (1989/1990) by David Caute.

From abebooks.com:

"Michael is almost 12 when Veronica, introduced to him as his cousin,
comes to live with the family. She is 15, mysterious, beautiful, and
indulgent toward Michael's awakening sexuality. By the time he finds
out she is his half-sister, he is too far gone to care. Forty years
later the youthful illicit relationship threatens to ruin Michael's
successful political career."
http://www.abebooks.com/servlet/BookDetailsPL?bi=563892766

From Amazon.ca:

"From Publishers Weekly...
 Michael Parsons falls "instantly in love" with his South African
cousin Veronica when she comes to London in 1939 to live with his
family. By the time his parents die in WW II, he knows that V is his
half-sister. He justifies his passion via entries in his journal that
record historical incidents of sibling incest and its endurance as a
classic theme, copiously citing the Jacobean tragedy 'Tis a Pity She's
a Whore and Ibsen's Ghosts . Determined to destroy his rival, V's
American soldier fiance, Mike stoops to deceit and trickery. When V is
hurt in a bomb raid and becomes dependent on barbiturates, her
inhibitions abate and her mind deteriorates. Mike tenderly cares for
her as their love flowers. Years later, Mike, now a Tory cabinet
minister under Thatcher..."
http://www.amazon.ca/exec/obidos/ASIN/1559701013

More used copies at abebooks.com:
http://www.abebooks.com/servlet/SearchResults?y=0&tn=Veronica%2C+or%2C+The+two+nations&bsi=0&x=0&prevpage=2

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search strategy:
abebooks.com advanced search: author: david / title: veronica

Thanks.