Solutions to be Clued by Waterloo

This was a quite straightforward puzzle whose theme was unequivocally stated in the preamble: in some cases the "clue" was actually the answer to a clue to be derived. Gregson was expecting something a little more inventive from this idea - well-known phrases, perhaps, that could be read as wordplay, but the derived clues were on the whole pedestrian, if terse and fair. The preamble's admonition to find the "simplest" clue in each case seemed unnecessary. Who's to say some of these words mightn't allow of a simpler clue, however that's to be measured. In any case, Waterloo provided an amusing evening's diversion.

Across
1 Fish very old ship gets into oldish ship (6)
SARGOS (ARGO inside SS)
6 Endless fortune belonging to a Juno (6)
LUCINA (LUCK minus last letter + IN + A)
11 Unit (13, four words)
ONE ON ONE TIME (UN + I (one) + T(ime))
13 Stop and have pasta, cutting off the ends (5)
AVAST (HAVE PASTA minus first and last letters)
15 Check once, remove knight and put it back (4)
STET (STENT = stint = check minus N (knight))
16 Preserve (12, three words)
KEEP PENNY ICE (P(enny) + RESERVE)
17 Take the same case, end first, and bore (5)
EAGRE (AGREE with last letter moving to beginning)
20 Girl moving right along without a fault (4)
PURE (PRUE with R moving one letter to the right)
21 Willed (11, three words)
TWO BOYS LEFT (WILL + ED)
24 Plant with a stalk (4)
SETA (SET + A)
25 Less than a small monastery, but more than a yard long ago (3)
ELL (CELL minus first letter)
26 Plainsong, not northern hymn, twists believer's tongue (4)
PALI (Jumble PLAINSONG minus N SONG)
27 Bathes (12, four words)
DIPS MAD MAN IN (HE inside BATS)
29 It means two (4)
TWAY (T (it) + WAY (means))
A very elegant and terse clue.
33 Amount of dry goods needed for making bread (5)
ARDEB (Anag. BREAD)
34 Spurious clamour in dismay, interrupted by broken "Oh!" (10)
APOCRYPHAL (O, H inserted separately into CRY inside APPAL)
37 In box postpone first greedy look (4)
OGLE (LOGE with first letter moved)
That's the third example of this "letter moving" wordplay.
39 Characters love sport which involves no energy (5)
OGAMS (O + GAMES minus E (energy))
40 Rams (13, four words)
SHEEP UP IN ARMS (Anag. ARMS)
41 Held bow on the lookout (6)
TENTIE (TEN = Tenuto, musical direction, + TIE)
42 Random opening can result in this time being delayed in shops (6)
SORTES (STORES with T moving)
...and yet another example.

Down
1 Slot (13, three words)
SOCKET SET LOST (Anag. LOST)
2 Advance payment, if returned, might destroy property (4)
ANTE (ETNA (property destroyer when erupting?) rev.)
3 Undisciplined end of savage East Bengal riot, not necessarily final (12)
RENEGOTIABLE (Jumble E (last letter of SAVAGE) + EAST BENGAL RIOT))
4 Work and work to produce soggy mess (4)
GOOP (GO + OP)
5 Almost understand precise compartment of vaulting (6)
SEVERY (SEE minus last letter + VERY)
6 Places for milking Ayrshires, say, there's the answer (5)
LOANS (LO + ANS)
7 Radical society losing in due course and one ultimately traditional (5)
CETYL (SOCIETY minus SO (in due course) minus I (one) + L (last letter of TRADITIONAL)
8 Single opponents of many parts, not British (3)
ITS (BITS minus B)
9 Bird coming back after American prince (5)
AMEER (AM (American) + REE rev.)
10 Captivated (13, three words)
NETTED IN BLISS (Two meanings)
12 Harm (12, four words)
IT CUT AND HURT (CHARM minus first letter)
14 Betray, keeping note and short piece of hair (5)
SNELL (N inside SELL)
18 Struck before getting married (4)
AWED (A (before) + WED)
19 Long time no see -- practically ridiculous (4)
EONS (Jumble NO SE(e))
22 Attempt at word meaning "mysterious person" -- mother, say (4)
EGMA (E.G. + MA)
23 Movement almost makes way (4)
PLIE (PLIES minus last letter)
25 Sink kisser coming back after space (5)
EMBOG (EM + GOB rev.)
28 Under misapprehension, stripped to skin (6)
DERMIS (Hidden inside unDER MISapprehension)
30 Blame courageous creature (5)
WIGHT (Three meanings)
31 Initiate e-pawn's control in the centre (5)
EPOPT (E + P(awn) + OPT)
Unsure where the OPT comes from.
32 Cry when flushed player outbid another (5)
SCAPE (S + CAP + E (S, E bridge positions))
35 Perhaps conference president drops first two elements of keynote and loses head (4)
PEAR (SPEAKER minus KE minus first letter)
36 Second half of dinner, perhaps, coming before first dancer (4)
ALME (MEAL with two halves reversed)
38 King escaping very good Scottish peepers (3)
EEN (KEEN minus K)