4064 Metrical Variations by Hedge-sparrow

This was a very nice puzzle with the theme shown in the answer to 41 – EINSTEIN. The additional letters in wordplay gave TIME DILATION – LENGTH CONTRACTION. This explained how the across answers had to be entered. The letter T was doubled and double LLs were halved. The unclued entry was SPEED OF LIGHT. Einstein’s theories are barely understood by this Gregson but it was easy to check that the symbol for the speed of light is the letter c. In the completed grid the solver could discern the words SPECIAL RELATIVITY in the shape of a C.

Extra letters in wordplay are shown in [ ]

Across
4 Boy consumes too much old-fashioned oatmeal porridge (7)
POTTAGE OTT in PAGE
10 Inhale drug excessively (3)
TOO 2 definitions TOO[T]
12 Prevent young child going after cattle (5)
AVERT AVER (cattle) + [I]T
13 Old mixed diamonds provide temptation (6)
ENTICE [M]ENT (mixed) + ICE
14 Low temperature meeting place (4)
MOOT MOO + T (temperature)
15 Support a tree ... (3)
TEA TE[E] + A
17 ... a thorny tree bearing a lump containing parking ticket machine (9)
BELL-PUNCH P (parking) in BEL + LUNCH (lump)
18 Hearts taking on incompetent team - hardly a level playing field! (8)
HILLSIDE H (hearts) + ILL + SIDE
21 Spread out greyish-brown scroll (6)
UNROLL [D]UN + ROLL
22 Bright girl removing tail from large petrel (4)
NELL NELL(y)
25 Attractive young woman's an object of worship to lecturer (4)
DOLL [I]DOL + L (lecturer)
28 Strongly in favour of demand: "Leader of council must go!" (6, two words)
ALL FOR CALL FOR less C (1st letter of COUNCIL)
30 Follow softly an Australian snake (6)
TAIPAN TAIL (follow) + P (softly) + AN
33 15? 15 at the Ritz, perhaps? (6, two words)
EAT OUT Cryptic cluing with out used as an anagram indicator, Thus TEA is an anagram of EAT
35 Mark return of contemptible person (3)
DOT TO[A]D reversed
36 Hot stuff? Cool it! (6)
CHILLI CHILL I[T]!
37 Coward, very reprehensible, meeting International Academician on leave (8)
VILLIAGO V (very) + ILL + I (international) + A (academician) + GO
39 Big cats, head-to-head, going after master mason's rubble (7)
MOELLON M (master) + LEO (rev.) + L[I]ON
40 Concede acting Lord Lieutenant's returning to court (5)
ALLOW A (acting) + LL + WO[O] reversed
41 Playing tennis engrosses a German scientist (8)
EINSTEIN Anagram TENNIS containing EI[N]
 
Down
1 Restores street permits (5)
STETS ST (street) + [L]ETS
2 New environmental technology investigator initially backing information service (3, abbrev)
ITN N (new) [E](nvironmental) T(echnology) I(nvestigator) all reversed
3 In France, public office not taking on English learner after end of March (5)
HOTEL (marc)H + [N]OT + E (English) + L (learner)
4 Idle type verbally attacked in Post Office (6)
POTATO [G]OT AT in PO
5 Bit of armour plate on skirt is silent (4)
TACE 2 definitions
6 Pair of rollers damaging pelmet (6)
TEMPLE Anagram PELMET
7 Suffer pains to get me in Irish breeches (6)
TROUSE US in T[H]ROE
8 A sound from a bell carries on harmonising (7)
ATONING ON in A TING
9 End drops off Jock's adze easily, according to Edmund (4)
EATH EAT[C]H(e)
11 Coarse king - unctious (not half) and lacking in charm (6)
RIBALD R (king) + [O]I(ly) (unctuous) + BALD (Famous typo in this clue)
16 Poor quality work shows up in colour (6)
TINPOT [U]P in TINT
18 Boat-builder coming round in the morning knocked back a ritualistic drink (5)
HAOMA AM in [N]OAH reversed
19 As a joke, fool around with endless supply of money (5, two words)
IN FUN NI[T] reversed + FUN(d)
20 Dissuade French from appearing on film without beginning to swagger (6)
DEHORT DE (from in French) + (s)HORT
23 Kinsman's high spirits (7)
ELATION 2 definitions [R]ELATION
24 Finally place a bet - about four thousand pounds, initially (6)
LASTLY LAST (4000 lb) + L[A]Y
26 Names bird sitting on line and second turning up (6)
TITLES TIT (bird) + (SE(C) +L reversed)
27 Impaired pistol shot (6)
SPOILT Anagram PISTOL
29 American poem written up by colonial type - one from Asia Minor (6)
LYDIAN IDYL reversed + AN[T]
31 African tree conceals a creature (5)
KOALA A in KOLA
32 Check over trace of whisky stolen in Scotland (5)
STOWN W(hisky) in S[I]T ON
33 Shakespearean to augment majority of evoked memories (4)
ECHE ECH[O]E (s) reversed
34 Cabinet in exhibition displays part of fork (4)
TINE Hidden
38 Gazelle from part of Western India (3)
GOA 2 definitions