Susan Cooper's superb YA series, 'The Dark is Rising,' ('Over Sea, Under Stone,'. -Cornwall 'The Dark is Rising,' - Buckinghamshire. 'Greenwich,' - Cornwall, 'The Grey King,' and, 'Silver on the Tree,' - both Wales, but the latter includes a scene in the Lost Land of Welsh mythology). Ignore the dreadful film - Cooper felt suicidal after its release, but the backlash from three generations of infuriated readers brought her back from the brink.
Toby Frost is too modest, while not set in Britain, but on the various worlds of the British Space Empire and its enemies, his, 'Space Captain Smith,' novels are well worth a look (I'm re-reading them while the library's closed over Christmas).