PS by Homer

Homer's puzzle was based on the poem Night Mail by W.H. Auden. The relevant lines from the poem read:

This is the Night Mail crossing the Border
Bringing the cheque and the postal order
Letters for the rich, letters for the poor
The shop at the corner, the girl next door

Initial letters of redundant words in the clues spelt out the poet's full name: Wystan Hugh Auden. Various elements of the poem appeared in the four corners of the grid and were clued without definition:

1A = CHEQUE
5A = HTICEHR (Letters to the rich)
12A = HOPOTRE (Letters to the poor)
42A = THE MARY
44A = SHOPANN (42 and 44 together depicting "The shop at the corner" and "the girl next door)
45A = ALOPST (Letters of Postal in alphabetical order - i.e. Postal order)

Finally "Night Mail" could be seen crossing the Border in the finished grid, and these were to be highlighted. The near-appearance of Beattock completely passed Gregson by.

The thematic elements were elegantly arranged, but Gregson always feels a sense of unease when different elements are handled differently as here, since each one must be separately solved and gives little help with the others. Non-words in the grid require the wordplay to be crystal clear and unambiguous. Still this was an enjoyable and fair puzzle.

Across
1 Old chess piece, but not the rook (6)
CHEQUE (CHEQUER minus R(ook))
5 Decoy with royal clothing appears before queen (7)
HTICEHR (TICE inside HH + R (queen))
10 [Wily] little Henry's a handful (4)
HANK (Two meanings)
12 Dance of the sun-god (7)
HOPOTRE (HOP + O(f) + T(he) + RE)
14 Sardelle lacking resistance -- free meal for linnet (7)
ALL-SEED (Jumble SARDELLE minus R)
16 Disturbed [young] animal's left shed at full pelt (5)
AMAIN (Jumble ANIMAL minus L)
17 Rector copies missing folio and reaches out for the Edinburgh edition (5)
RAXES (R(ector) + FAXES minus F)
19 One forsaking certain brew that's served up by Hebe (6)
NECTAR (Jumble CERTAIN minus I)
20 Sort of tunic, attention getter adopted by [Shanghai] triad for example (7)
CHOROID (OI inside CHORD)
21 What can be cut by sickle, trimmed by fellow (5)
SHEAF (SHEAR minus R + F)
23 Lesson you and I skipped when translating Marlowe (5)
MORAL (Jumble MARLOWE minus WE)
24 Vicar with centre parting restyled hair from bun (4)
VAIR (Jumble VICAR minus middle letter)
27 Starts to collapse after nine [troublefree] years, like some furniture (4)
CANY (First letters of COLLAPSE AFTER NINE YEARS)
29 A measure of narrow, I'd think, could describe this (5)
WIDTH (Hidden in narroW ID THink)
30 [Ankle] joint on a horse or sheep (5)
JACOB (J + A + COB)
33 After source of bubbly? Maybe get to a _____ (7)
BOTTEGA (First letter of BUBBLY + jumble GET TO A)
34 Allied advance injured [Norway's] agent (6)
AGNATE (A + jumble AGENT)
37 Result of deforming venae (5)
NAEVE (Anag. VENAE)
40 Scatter kails about (5)
STROW (WORTS rev.)
41 Bohemian lass, half cut and turning catty (7)
BEATNIK (BEATRICE minus second half + KIN rev.)
Gregson was misled for a long time assuming the Bohemian lass to be Mimi, and the answer to be some variant of MIAOW, and windered if this misdirection
was deliberate.
42 Short thesis on a railway (7)
THEMARY (THEMA + RY)
43 Chop [hard] neeps, then mash for Dolly (4)
PENE (Jumble NEEPS minus last letter)
44 Nosh cooked in eg, wok? No, quite the reverse (7)
SHOPANN (PAN inside jumble NOSH)
45 Leading soprano one sees work in a high tone (6)
ALOPST (OP + S(oprano) inside ALT)

Down
1 Port Authority avoids ministers in tugs (6)
CHAINS (Chaplains minus PLA (Port of London Authority))
2 Draw hearts before last singleton's discarded (5)
HALVE (H(earts) + A (before) + LIVE minus I)
3 Embrace couples from England, Scotland and France (6)
ENLACE (Two letters each from ENGLAND, SCOTLAND and FRANCE)
Though the clue give no indication as to which two in each case
4 Such as Stateside drug king might supply (4)
USER (US + E + R)
6 Draw out nail securing nothing (4)
TOZE (Z inside TOE)
7 Hollow [urn], capacity equivalent to 4 bushels, or 6 (4)
COMB (Three meanings)
One being a reference to 6 down.
8 [Gravity] measurement apparatus a lecturer employed in college (6)
ETALON (A + L(ecturer) inside ETON)
9 A trendy new term (7)
RENT-DAY (Anag. A TRENDY)
11 Mary Rose, ship of undetermined value and wreck, gets weapons again (6)
REARMS (Jumble MARY ROSE minus O(f) and Y)
13 For the whole choir's religious education, sanctimonious one turned up (7)
RIPIENO (RI + PI + ONE rev.)
15 Weigh Arab's heavy instrument (5)
SITAR (SIR + AR)
18 Buck's aching for the Listener [answers] (4)
SOAR (Homophone SORE)
20 Volunteers carry small boar for Cutty Sark? (5)
COTTA (COT + TA)
22 What magpie acquired and left amid call of dismay (7)
HAPORTH (PORT inside HAH)
24 They hammer out [unusual] tunes, six pieces containing a hint of Strauss (7)
VIBISTS (VI + first letter of STRAUSS inside BITS)
25 Periodically oblige one being couthy (4)
BIEN (Alternate letters of OBLIGE ONE)
26 [Devil] plundered holy book collection in Slough (6)
SHAVED (AV inside SHED)
27 Shut up about flipping [Essex] girl (5, two words)
CAN IT (C + TINA rev.)
28 Metal plate engineers introduced to broken toes (6)
STEREO (RE inside jumble TOES)
31 Tom's preference in bed? A short sleep, not otherwise (6)
CATNEP (CAT NAP with NE replacing NA)
32 Old Bill nabs tense prop for loose tackle (6)
BECKET (BECKE + T)
35 Language used by Nova Scotia and parts of Scotland (5)
TWINS (TWI + NS (Nova Scotia))
36 Run -- formality, taking leader out of sight? (4)
ROMP (R + POMP minus first letter, & lit?)
38 [New] element found in Cairngorms (4)
AIRN (Hidden in cAIRNgorms)
39 Sandwich perhaps the Spanish stuffed with bits of alubias rojas (4)
EARL (First letters of ALUBIAS ROJAS inside EL)