The Canadian Enclycolpedia say this about the "early" organ works of Healey Willan (1880-1968): With the music for organ one enters a different world. Here Willan was thoroughly at home and made a significant and lasting contribution. One work stands out: the monumental "Introduction, Passacaglia and Fugue" of 1916. It represents the culmination of Willan's first period of organ composition, which started ca 1906 with a Fantasia on 'Ad coenam agni.' The Preludes and Fugues in C minor and B minor and the "Epilogue" are the other major works from this period. While not exploring the possibilities of the instrument as searchingly as his masterpiece, they are idiomatic and very typical of their time. They combine an innate Englishness (with a Stanfordian flavour) and a European chromaticism that can be found in Reger and Karg-Elert. (Willan knew and played a few pieces by the latter, but it is doubtful he had heard much Reger at the time he was writing these pieces.)
The second work in the trilogy is the "Aria and Fugue". It is a quiet, romantic work with a lovely cello-like melody in the "Aria", followed by a light and flowing "Fugue".
A recent article on Willan's music said that the "Fugal Trilogy" said that "while perhaps not inspired, is certainly not mundane, and proves that Willan could could construct a convincing fugue at the drop of a hat!