Almost all major American trade and university presses have some works on
British history on their list. Quite a few of them, of course, are
American editions of books that are published in Britain as well, most
but not all by British authors. Among trade publishers I would suspect
that W.W. Norton and Knopf have, perhaps, more British titles than other
trade publishers, but so too do Viking, Penguin, and Dutton (all owned by
Pearson). Among university presses I would suspect that Yale, Harvard,
Stanford, California, North Carolina, might be higher than most, but
this is very much an impressionistic response. Interest in Britain is no
doubt in decline in the States but still many publishers will still have
some British representation.