A well above average Jumbo, I felt, with the usual preponderance of straight-down-the-line clues pleasingly peppered on this occasion with a nutritious selection of &lits, reverse cryptics and just plain quirky meta-offerings. Many things in contention for COD, but I'll give my award to 35dn as I always enjoy the breaking of the fourth wall, if indeed crosswords can be said to have walls. I'll leave it to the readership (that's you) to enumerate some of the other splendid clues in this grid - many thanks setter, for some real cryptic belters!
ACROSS
1 Side holding power in a splinter group (6)
ASPECT - P [power] in A SECT [a | splinter group]
4 Underworld boss having mobile that goes on by itself (10)
PERSEPHONE - PHONE [mobile] that goes on PER SE [by itself]
10 Go to form new colony as part of vicious war, maybe (5)
SWARM - hidden in {viciou}S WAR M{aybe}
14 Getting hump somehow in ordeal is characteristic of success (9)
TRIUMPHAL - (HUMP*) ["somehow"] in TRIAL [ordeal]
15 Strange edict about one article after another penned by relative is shown to be true (13)
AUTHENTICATED - (EDICT*) about A [one article] after THE [another (arcticle] "penned" by AUNT [relative]
16 Refuse to admit learner that’s less developed (7)
LITTLER - LITTER [refuse] to "admit" L [learner]
17 On foot, it provides quick cover (7)
TOENAIL - cryptic def: quick as in the part of the foot under the nail.
18 Cruciverbalist’s last kind of wordplay, having put out third puzzle (7)
TANGRAM - {cruciverbalis}T + AN{a}GRAM [kind of wordplay, "having put out third" (letter)]
19 Avoiding offence, in a way — like copper, initially (11,7)
POLITICALLY CORRECT - referred to be the initials PC, just like a Police Constable is.
21 Behave like obsequious dog or other little animal (4)
FAWN - double def
24 Decide not to run with small old-fashioned weapon (5)
SPIKE - S PIKE [small | old-fashioned weapon]. As in "to spike an article".
26 Investor finally compensated, holding current issued shares (8)
RATIONED - {investo}R ATONED [compensated], "holding" I [current]
27 Make from sale, having also included promotional activity (8)
BRANDING - BRING [make from sale], having AND [also] included
29 Result of making name for oneself as fighter (3,2,6)
NOM DE GUERRE - cryptic def
30 What can be got from what’s in menu, in short (11)
NOURISHMENT - (MENU IN SHORT*) ["what can be got from what's in..."], &lit
32 Rock group worth breaking up? Not so far (6,5)
STONE'S THROW - STONES [rock group] + (WORTH*) ["breaking up"]
35 Cut back — result of freeze, say — in authoritarian regime (6,5)
POLICE STATE - reversed LOP [cut] + ICE STATE [result of freeze | say]
37 Respite, as European is accepted by British fairly (8)
BREATHER - E [European] is accepted by B RATHER [British | fairly]
39 Bad fortune besetting European — score reduced by six (8)
FOURTEEN - (FORTUNE*) ["bad"] "besetting" E [European]. Score as in "twenty".
40 Something outstanding about university’s appearance initially (5)
DEBUT - DEBT [something outstanding] about U [university]
43 What’s the matter with intelligence? Poet’s pronouncement (4)
GREY - homophone of GRAY (Thomas, 1716-1771, of Elegy Written In A Country Churchyard fame). Grey matter is "the matter with intelligence".
44 It’s half a world away from where we are here (8,10)
SOUTHERN HEMISPHERE - cryptic def. Rather assuming that the solver is not in Australia!
47 Improperly dispensed upscale form of medication (7)
CAPSULE - (UPSCALE*)
48 Fruit was revolting with it (7)
ROSEHIP - ROSE [was revolting] + HIP [with it]
50 King protected by subjects in heated situations (7)
TROPICS - R [king] "protected" by TOPICS [subjects]
51 Enjoying, for example, cricket? Over count is repeatedly revised (13)
INSECTIVOROUS - (OVER COUNT IS IS*) ["revised"]
52 Fifteenth century house in city (9)
LANCASTER - double def
53 In peculiar way, how swindler is selected for side? (5)
ODDLY - reverse cryptic of S{w}I{n}D{l}E{r}
54 Full of amazement since a lot of weight I lost (10)
ASTONISHED - AS TON I SHED [since | a lot of weight | I | lost]
55 Oblivion achieved ultimately in drink in this? (6)
BENDER - {oblivio}N {achieve}D, in BEER [drink], semi-&lit
DOWN
1 Wild animals run into stakes (9)
ANTELOPES - LOPE [run] into ANTES [stakes]
2 Painters initially list oil in mixed medium art technique (11)
POINTILLISM - P{ainters} + (LIST OIL IN*) ["mixed"] + M [medium]
3 Left in piece of jewellery on time for royal court (7)
CAMELOT - L [left] in CAMEO [piece of jewellery] on T [time]
5 Report written up about century, brilliant effort (5)
ECLAT - TALE [report] reversed about C [century]
6 House of Lords, perhaps, having ethos tamely changed (7,4)
STATELY HOME - (ETHOS TAMELY*)
7 Confuse pagan with theory of ancient philosophy (11)
PYTHAGOREAN - (PAGAN + THEORY*)
8 See way to support past master, above all (8)
OVERLORD - LO RD [see | way] to support OVER [past]
9 Motor vehicle, say, in competition overturned (6,3)
ESTATE CAR - STATE [say] in reversed RACE [competition]
10 Behind one's back (6)
SECOND - double def
11 Later adjusted temperature in simple option (11)
ALTERNATIVE - (LATER*) ["adjusted"] + T [temperature] in NAIVE [simple]
12 Subject of most original palindrome? (5)
MADAM - I think this is a cryptic reference to "Madam, I'm Adam", allegedly the first palindrome spoken, in the Garden of Eden after the creation of Eve.
13 Current malfunction in LA? (5,7)
SHORT CIRCUIT - reverse cryptic, as a LA{p} is a "short" circuit.
20 Scholarly American's volume found on a railway (8)
LITERARY - LITER [American's volume] found on A RY [a | railway]
22 Female article of clothing close, along with male one (7)
NIGHTIE - NIGH [close], along with TIE [male (article of clothing)]
23 Motivated in this way with drug, in conclusion (8)
ENTHUSED - THUS [in this way] + E [drug], in END [conclusion]
25 Take part in novel event held after ten (8)
ELEVENTH - hidden in {nov}EL EVENT H{eld}
28 One seeing what’s going to be charged for sweet (5,3)
BULL'S EYE - if you're about to be charged by a bull, the thing seeing what's going to be charged (i.e. you) is the bull's eye!
29 What contains primarily oats, say, easily being consumed by horse? (7)
NOSEBAG - O{ats} S{ay} E{asily} B{king}, "consumed" by NAG [horse], semi-&lit
31 Popular with constituents, including female relative that’s erratic (12)
INCONSISTENT - IN [popular] with CONTENT [constituents], "including" SIS [female relative}
33 Given too much publicity about European vote presented (11)
OVEREXPOSED - OVER E X POSED [about | European | vote | presented]
34 Golf clubs holding English Open, finally — competitors don’t want it (6,5)
WOODEN SPOON - WOOD & SPOON [golf clubs] "holding" E [English] + {ope}N
35 Reduce new academic work that immediately follows this (11)
PARENTHESIS - PARE N THESIS [reduce | new | academic work]. The parenthesis follows the clue, containing its enumeration!
36 Moderated about one part of speech being held up, in short (11)
ABBREVIATED - ABATED [moderated] about reversed I VERB [one | part of speech]
38 Specialized publications I create so cryptically (9)
ESOTERICA - (I CREATE SO*)
41 Manager of funds changed rate with more confidence (9)
TREASURER - (RATE*) ["changed] + SURER [with more confidence]
42 Sailor aboard sturdy launch (5,3)
START OUT - TAR [sailor] "aboard" STOUT [sturdy]
45 Liable to embrace sweet girl, initially, being vulgar (7)
PROFANE - PRONE [liable] to embrace F{anny} A{dams} (as in "sweet Fanny Adams")!
46 Forceful or pitifully weak about check (6)
PUNCHY - PUNY [pitifully weak] "about" CH [check]
47 Capital in company affected by inflation? (5)
CAIRO - CO [company] "affected by inflation", which is to say, filled with AIR
49 Cry holding son giving sign of life (5)
PULSE - PULE [cry] "holding" S [son]
