This puzzle's rather convoluted construction apparently derived from the intriguing discovery that the name Bela Lugosi, when decoded via a Playfair code square with the somewhat appropriate code word "Goulash", yields "SIULUOAGBE", i.e. a jumble of itself but for one letter. Gregson was in two minds about how impressive a feat this was. On the one hand there was a lot of inelegant shuffling of clues, clashing letters and hidden instructions to make it work as a theme. On the other hand he couldn't recall any other instance of Playfair-encoding yielding anything other than a meaningless sequence of letters. In any case, for any fan of Playfair puzzles (Gregson, for the record, can't get enough of them), this was an entertaining example.
Corrected letters in Across clues spelled out "Clashes are won by downs", which revealed which letter to enter where across and down answers disagreed, but didn't help with the cross-checking. Corrected answers in Downs spelled out "Order by clues and encode". The declared locations of clashing letters, and the unclued four-letter entries, gave away the locations of the four "loosely related individuals" appearing in the grid, at rows 1, 4, 10 and 15. But for the four-letter entry at the middle of each of these rows, the names Franz Lehar, Bela Bartok, Franz Liszt and Peter Lorre appeared, all distinguished Hungarians, as is Bela Lugosi, entered with a misprint as BEUA LUGOSI at 22A. These names provided the coded versions of the unclued entries and thus allowed the Playfair code square to be determined, with the code word "Goulash". Rearranging 22A in the order given by the jumbled ten down clues gave SIULUOAGBE, which Playfair-encoded back to Bela Lugosi, the answer to be (re-)entered at 22A.
Across
1 Grain stored in towers? A p[c]ity (4)
AGRA (GR(ain) inside AA)
AA seems to do service as "towers", inexplicably.
8 This found on beast and be[l]ast on this? (4)
HORN (Two meanings)
11 Caught, we got attached to central spot in Barlinnie ce[a]ll (5)
COOEE (C(aught) + OO (we) + EE (= Scottish eye = central spot))
12 Wife's clothing is not on earth suitable for lad or lad[s]s (6)
UNISEX (NIS (is not) + E(arth) inside UX (wife))
13 Gas that could w[h]arm limited space holding function (6)
ARSINE (SIN (trig. function) inside AREA minus last letter)
14 Opi[e]ning about TV... (5)
ONSET (ON + SET)
15 ...conten[s]t and expressing a couple of things heard (4)
DUEL (Homophone DUAL)
18 Si[a]p wine? It's nastier when bottled (7)
RETSINA (Anag. NASTIER)
An anagram well-known to Scrabble players.
19 Manuscript covers to be in French, perhaps a hundred of them in l[r]ace
(6)
METRES (ETRE (= French TO BE) inside MS)
21 Dick[e]'s cast (cheatingly) spades on trump (4)
SLUR (S(pades) + LUR (a form of trumpet))
24 R[w]ave's top dance band finishes early (4)
COMB (COMBO minus last letter)
27 See stamps in woman's ba[o]g (6)
LADIES (LA + DIES)
29 Kid[n] that is taken if a school withdraws support (7)
ADOPTEE (A + POD rev. + TEE)
A clue that suffers somewhat from the fact that the misprinted form works
almost as well.
34 Once r[b]efitted, boot knight out (4)
SATE (SKATE minus K)
35 Lost in southern state, for example, back in wild parts[y] (5)
ORGIA (GEORGIA minus E.G. rev.)
36 Hair gel isn't set? Less haste, perhaps - it's partly gell[d]ed
(6)
RIGLIN (Jumble HAIR GEL ISN'T minus HASTE)
37 Ru[o]mp joint - a minute quantity of Angus (6)
JAUNCE (J(oint) + A + UNCE)
38 Skin flab[w]s? I have a number rearward (5)
NAEVI (I'VE A N rev.)
39 See[n]ds up perhaps a foot (4)
APED (A + PED)
40 N[S] American runner runs most of qualifier (4)
RHEA (R(uns) + HEAT minus last letter)
Down
a Old sa[o]lve made from animal grease
ASSOIL (ASS + OIL)
b Respit[r]e's no good for old Irishman
REEK (GREEK (Irishman!) minus G(ood))
c Fugue I'll put together with r[d]eception in mind
GUILEFUL (Anag. FUGUE I'LL)
d Did compo[e]te provide less professional stews?
VIED (Jumble PROVIDE minus PRO)
e B[R]uddy's deep in memory
ROSEATE (SEA inside ROTE)
f New priest without digs breaking his tie[p]s
HINTS (N(ew) + PRIEST minus PRIES, inside HIS)
g Cardinal has operation for fl[e]u?
TENURE (TEN (cardinal number) + URE)
h Walk, not typically holding han[r]d
KNOTTY (Hidden inside walK NOT TYpical)
i Sw[c]otty at school? A condition acclaimed!
ACADEMICAL (Anag. A ACCLAIMED)
Again, the misprint was tough to spot since the clue almost worked as it
stood). "Scotty" to indicate a Scottish usage seems dubious.
j Od[l]d close to start of first round
FORBY (F (last letter of OF + ORBY (round))
16 Greek co[u]ed from these parts? Jumper's covering a nice bust
(10)
PARASCENIA (Jumble A NICE inside PARA)
Cute definition.
17 Polish duke starting out in bo[e]at (4)
DRUB (D(uke) + RUB)
20 Second XI batted, bringing end of game in one f[s]lick (8)
SLEEVEEN (Jumble S + ELEVEN + E (last letter of GAME))
21 Women's room cold[a]? (4)
SODA (Two meanings)
23 Day on which sub[n]'s powerful gauge registers unknown latitude
(70
SIZZLER (Z (unknown) + L(atitude) inside SIZER)
25 Where you might see bon[d]y girl, big and awkward - fever's less advanced
(6)
MORGUE (MOR (ungainly girl) + AGUE minus A(dvanced))
26 Si[e]t about a table, not skilful with food (6)
ATTACK (A + TABLE minus ABLE + TACK)
28 Es[n]treatment one's covering in silver (6)
ASKING (SKIN inside AG (silver))
30 B[c]oat? One in a public fountain (5)
PAINT (I inside PANT)
31 Shut up in a place that's hi[o]t, he split from thieves in a scuffle
(5)
STIVE (Jumble THIEVES minus HE)
32 L[D]aud France's rising standard (4)
FRAP (F(rench) + PAR rev.)
33 Language from p[e]ast city, old Dutch (4)
URDU (UR (old city) + DU(tch))