Charles Joseph Frost (June 20, 1848-October 13, 1918) was a pupil of his father at Tewkesbury Abbey, and of George Cooper, Sir John Goss (St. Paul's Cathedral, London) and Charles Steggall.
From 1865 he held various appointments as organist, the last being at St. Peter's, Brockley, beginning in 1884). There he founded a choral society in 1845. He received his Mus. Bac. in 1877, and his Mus. Doc., Cantab. in 1882, and was a Fellow of the College of Organists. He gave many concerts, recitals and lectures.
As a composer he wrote cantatas, oratorios, a symphony, and numerous organ pieces.
"Impromptu" is a very expressive work, tinged with sadness to be sure. Written in the key of A minor, it is chromatic and intense, but always gentle.
This piece struck as the "death of an autumn leaf," since it begins with vivid colors that fade as the work progresses.
At times we feel the wind blow, teasing the leaf, which is already fading and becoming frail. The wind seems to trick the leaf into being part of the dance, and the leaf, not realizing what is happening, succumbs and falls slowly to its death on the ground already covered by many of its fellows...
This work is found in Volume 2 of "The Organist's Quarterly Journal". The score itself is too large to attach, but THIS is the correct IMSLP link, where you can find 9 of the 10 volumes.
https://imslp.org/wiki/The_Organist's_Quarterly_Journal_(Various)
A photo Charles Joseph Frost is attached below, as well as two photos of At. Peter's Church, Brockley.