The opening of the symphony is dramatic. Against a pianissimo timpani roll on a bare 5th chord, the lower strings, pizzicato, play a slow chromatic theme consisting of a 3-note motif, and a number of further motifs which are clearly derived from it. The motif and its metamorphoses are very important: they will eventually dominate the finale, and before then they reappear in reappear more than once in different guises. The motif spans a tritone; this interval is destined to play an increasingly important part as the symphony progresses.

The development itself is short and very complex, mainly contrapuntal, with the themes greatly metamorphosed and the contrapuntal lines in several keys at once. But at bar 143 the sound abruptly fades to nothing, as when a radio is switched off, and we hear, in a dreamlike state, the notes of the introductory theme on flute, oboe, glockenspiel and harp, while the violas play a languishing chromatically descending motif, and quietly stalking arpeggios in strange tonalities are heard from cellos end basses. It is as if the unconscious were suddenly exposed. Episodes of this type occur often in Brian’s symphonies, where the external clangour suddenly disappears and the mood turns, as it were, to one of inner contemplation. Here, in the shadows, we hear the slow chromatic theme from the very beginning, quiet but firm, with a hint of menace. It is still there, and will return.
Just as suddenly, we are plunged back into the development, this time of the second subject group.  The recapitulation, when it comes, seems fairly orthodox, though the themes are presented in rich new orchestrations that are entirely Brian's own. But at the conclusion of the final theme comes, not the expected coda, but a passionate outburst in which the first two motifs of the opening theme, the second modified by a passing-note, ring out fortissimo, like the sudden materialising of some dark power. As the sound fades, the bass instruments mutter a widely-spaced mutation of the opening three-note motif, and the movement closes with a sombre reiteration of the opening timpani chord.

In this first movement the themes are orthodox enough: even the first, passionate theme, with its wide span and violins in thirds, belongs to a world not far from that of Elgar’s Second Symphony; and the orchestration of the exposition is fairly traditional, though Brian produces some interesting timbres - for example the pairing of muted cellos and clarinet at the octave at bar 108, ushering in the muttering, on strings that grow and erupt into the development. The texture of the development is far from orthodox, however, abounding in a highly individual kind of polytonal counterpoint that Brian made his own.