Thanks to the link from #, I was able to find and copy the applicable text from The Classical Music Lover's Companion to Orchestral Music, by Robert Philip (Yale University Press, 2018 - pp 214 ff.)

BRIGG FAIR: AN ENGLISH RHAPSODY (Frederick Delius (1862-1934)

In 1905, at the North Lincolnshire Music Competition held in the market town of Brigg, Joseph Taylor, aged seventy-one, won the newly established folk song section with his performance of ‘Creeping Jane’. The singing of traditional songs was in decline, and the Folk-Song Society had been founded in 1898 to collect them before they vanished. One of the Society’s leading members was the composer Percy Grainger. He had encouraged the inclusion of folk songs in the Brigg competition, and was there to note them down.
After the competition, Taylor came to him and sang him ‘Brigg Fair’, which he had known since he was a child, and three years later Grainger recorded Taylor singing it, on a wax cylinder. Struck by the beauty of the song, Grainger arranged it for tenor solo with chorus, adding extra verses, and this version was performed at the Brigg competition in 1906. The following year, Delius was deeply impressed by Grainger’s arrangement of ‘Brigg Fair’ and asked permission to use the tune as the basis of an orchestral work of his own.
The result was this ‘English Rhapsody’, which Delius dedicated to Grainger.
Joseph Taylor travelled to London to attend the first London performance in 1908 and stayed with Grainger and his mother, ‘delighting us with his personality, which was every bit as sweet and charmful as his singing’, as Grainger remembered. At the performance, ‘When the “Brigg Fair” tune was given out at intervals by the English horn and other instruments of the orchestra, old Taylor gently “joined in” with his sweetly ringing tenor voice, to the amazement of the audience.’4
Delius’s score, published in Germany in 1910, includes six stanzas:

BRIGG FAIR

It was on the fifth of August
The weather hot and fair
Unto Brigg Fair I did repair
For love I was inclined.

I got up with the lark in the morning
With my heart so full of glee,
Of thinking there to meet my dear
Long time I wished to see.

I looked over my left shoulder
To see whom I could see
And there I spied my own true love
Come tripping down to me.

I took hold of her lily white hand
And merrily was her heart,
And now we’re met together
I hope we ne’er shall part.

For it’s meeting is a pleasure
And parting is a grief,
But an unconstant lover
Is worse than any thief.

The green leaves they shall wither
And the branches they shall die
If ever I prove false to her,
To the girl that loves me.

Delius may or may not have known that only the first two stanzas were from the original song sung by Taylor. The rest had been assembled by Grainger from other traditional songs in order to make a more complete narrative.
Grainger, in a programme note for Delius’s rhapsody, encapsulated the appeal to both composers of the melody and its (elaborated) text: ‘a late-summer dream of morning freshness, love, peacefulness, quiet rural jollity, lazy church bells and the glowing English country-side’.5 The words of the song are happy, and Joseph Taylor in his 1908 recording sings the opening verses with a dancing lilt. To musicians reared on major and minor scales, however, the melody has an ambiguity of mood, as so many songs in the old modes seem to (‘Brigg Fair’ is in the Dorian mode). It is this that both Grainger and Delius exploit to create music full of nostalgia and a sense of impermanence – the ‘evanescence of beautiful things’, as Philip Heseltine put it.
Delius’s work is scored for large orchestra, including fourteen woodwind and six horns. These are used to provide a wide range of delicate effects, only occasionally coming together for grand climaxes. Most of the piece consists of a set of variations on the melody of ‘Brigg Fair’, interspersed with contemplative passages. The opening sets a pastoral scene: a solo flute plays arabesques, accompanied by the lightest of harp arpeggios and ppp string chords. It inevitably calls to mind the opening of Debussy’s Prélude à l’après-midi d’un faune, but the sensuousness of Delius’s flute is less erotic, more rustic. As it continues it becomes more bird-like, and is joined by another flute and a clarinet as if from neighbouring trees. This gives way to the melody of ‘Brigg Fair’ on oboe, accompanied by clarinets and bassoons, followed by a set of variations on the theme. The flute takes it up, accompanied by strings, and the harmonies become more complex (they have had a nostalgic depth even from the opening bars). Then it moves to the strings in chorus, joined the next time round by flutes and clarinets. Now the melody begins to dance, with a tripping counterpoint in the violins. The counterpoint moves to flute and clarinet while horns take up the tune, and then a trumpet takes the melody to the first climax of the piece. The mood calms, and the opening flute arabesque returns for a moment.
This is the beginning of an interlude. Over quiet, sustained chords, the violins sing a rising phrase, as if stretching out the opening of ‘Brigg Fair’. This little motif is repeated and developed. It passes to cor anglais, and then to a horn, all the while cushioned by the slowly shifting harmonies below. The effect is like a sustained meditation on a fine summer’s day. From the calm emerges another variation of ‘Brigg Fair’ on clarinet, with its rhythm evened out and with counterpoint on cor anglais, bass clarinet, bassoon, and horns.
The effect is mellow and even ecclesiastical – a bell sounds at the end of the tune. The strings join for the next variation, and the bell sounds again. The tune changes back to its original rhythm, but now in a broader three-time, and with a new counterpoint in the violins. This rises to a climax and falls away. The tune changes again, losing its swing, and becoming a solemn procession on trumpet and trombone, punctuated by string chords and the sounding of the bell (‘slow: with solemnity’). The processional melody moves to the violins. Then there is another brief interlude, as reminders of the opening flute solo are interspersed with fragments of the tune. The woodwind return to the dancing lilt of ‘Brigg Fair’ (‘gaily’). The cellos sing it, and the whole orchestra joins in. After a moment of hesitation, the music gathers energy, accelerates, and rises to a great climax at which the bells sound, and the tune is transformed into a blazing brass chorale. Gradually the climax falls away, an oboe gently plays the tune for the last time, and with a final reminder of the opening flute arabesques, the piece comes to a quiet close.

Delius: Brigg Fair, 1953 performance by the London Symphony Orchestra
https://www.youtube.com/watch?v=PMh2R4kRcFI