From his Paris Review interview. Emphasis is mine.

INTERVIEWER: What about England, where you spend part of each year? Is that a possible source of fiction?

ROTH: Ask me twenty years from now. That’s about how long it took Isaac Singer to get enough of Poland out of his system—and to let enough of America in—to begin, little by little, as a writer, to see and depict his upper-Broadway cafeterias. If you don’t know the fantasy life of a country, it’s hard to write fiction about it that isn’t just description of the decor, human and otherwise. Little things trickle through when I see the country dreaming out loud—in the theater, at an election, during the Falklands crisis, but I know nothing really about what means what to people here. It’s very hard for me to understand who people are, even when they tell me, and I don’t even know if that’s because of who they are or because of me. I don’t know who is impersonating what, if I’m necessarily seeing the real thing or just a fabrication, nor can I easily see where the two overlap. My perceptions are clouded by the fact that I speak the language. I believe I know what’s being said, you see, even if I don’t. Worst of all, I don’t hate anything here. What a relief it is to have no culture-grievances, not to have to hear the sound of one’s voice taking positions and having opinions and recounting all that’s wrong! What bliss—but for the writing that’s no asset. Nothing drives me crazy here, and a writer has to be driven crazy to help him to see. A writer needs his poisons. The antidote to his poisons is often a book.