Page fifteen of the book Elgar Studies. The passages mentioned are from The Apostles:

"The parallels of harmonic technique and expressive import in the three passages place Elgar firmly in the orbit of the Wagnerian and post-Wagnerian musical worlds."

Elgar almost quotes a passage near the end of the Tristan prelude in his second symphony and parallels have been pointed out between the famous melody which opens Elgar's first symphony and the opening melody of Parsifal. Incidentally, following this very expansive melody (rather unBrahmsian I would say: Brahms is altogether tighter) in A flat the music abruptly heads into a theme in D minor; the (tri-)tonal rupture this causes in the structure of the music is something Brahms would never try; curiously enough, it is a Mahlerian idea, and whilst Wagner too hadn't tried it, the idea of tonal ambiguity nonetheless places Elgar within the same ball park as Wagner.