He was temporarily paralysed, and suffered severe pain and bladder complications, including pyelonephritis,[2] and spinal tuberculosis that ultimately led to his early death.

In August 1942, he wrote an essay on the painter Walter Sickert which, published originally in Horizon, brought him to the notice of Edith Sitwell, in no small part down to his own cultivation of her attentions.

A close attention to aesthetics, be it in human behaviour, physical appearance, clothing, art, architecture, jewellery, or antiques, is also a recurring concern in his writings.

Fictional content aside, the point of origin of virtually all of his stories is biographical: they are often set in places he knew or had visited, and feature thinly-disguised, often deeply unflattering, depictions of friends, family and acquaintances (to the extent that over thirty years after Welch's death, his art school friend, the artist Gerald Leet, refused to contribute to Michael De-la-Noy's biography, where he is identified only as 'Gerald' in the index.[12][13]).

[17] Common themes in his art include objets d'art, cats, still lifes (often incongruously juxtaposed) and assorted gothic motifs, often in a fantastical landscape, although not in one of his most famous works, The Coffin House (1946) depicting a locally-renowned dwelling, north of Hadlow, Kent.

[18] Opinions on Welch's artworks have varied widely: amongst his biographers, Michael De-la-Noy and James Methuen-Campbell consider him to be underrated; in Robert Phillips' view his paintings are "lightweight" and his drawings "fussy and shallow".

In a perceptive review of the reproductions in A Last Sheaf, the un-named Times art critic remarked on the "whimsically sinister" qualities of Welch's depictions.

The writer noted that Welch's specific skill—that of the detached but perceptive observer—which is so evident in his writings, is lost in his art, where he inadvertently (and falsely) appears to present "himself [as] clever to like what most people would think preposterous.

"[21] A painting such as Now I have only my dog, ... is easy to remember and evidently the work of a man of unusual and definite character, but for all that it is painfully smart, and leaves precisely the impression of frivolity that the writings always manage to avoid.

[21]Following the reissue of the Journals, writer Alan Hollinghurst found in Welch's self-portraiture (of which there are several examples; one is in the National Portrait Gallery) a tendency to "amplify the over-riding concern of his writing to fix his youth forever while he accelerates towards death.

[25] In 1951 the English composer Howard Ferguson set five of Welch's poems (included in A Last Sheaf) as a song-cycle for voice and piano, entitled Discovery.

[30] Welch appears as "Merton Hughes" in the 1956 novel No Coward Soul, written by his friend, the painter Noël Adeney,[31] and as "Kim Carsons" in William S. Burroughs' The Place of Dead Roads.

Fellow student at Goldsmith's, Helen Roeder, called him 'Ariel',[37] and Maurice Cranston highlighted the complexity of Welch's character, at least in part influenced by his health.