Across:
1 The China nobody knows about is hidden (hidden china/delph dinner service = SECRET SERVICE) from those doing the snooping (SECRET SERVICE),
10 Union (European Union = E-U-) admits Quaker leader (‘Quaker’ leader = -Q-) is on your side (-ALLY) (EQUALLY) to the same extend (EQUALLY),
11 What’s in 21 across is similar (‘secret’ = PRIVATE) to what’s in the army (PRIVATE),
12 Assess (RATE) what’s in the Euphrates River (what’s in the ‘Euphrates River’ = RATE),
13 Girl (ANN-) discovers young one (boy) heading off (b) (‘boy’ without ‘b’ = -OY) (ANNOY) to get someone’s goat (ANNOY),
15 Paper (STAR) concealed customs tariffs (concealed ‘customs tariffs’ = STAR),
17 Curmudgeonly dumped lemon curd (‘curmudgeonly’ dumped ‘lemon curd’ = ugy = GUY) produced by gal’s partner (gal’s partner: ‘guys and gals’ = GUY),
19 Trade Union has got no idea (‘Trade Union’ has got no ‘idea’ = trunon = TURN ON) what it means to flick a switch (TURN ON),
21 One of the agents (SECRET agent) associated with all sides today (SECRET on sides of today’s grids),
22 Large country house (VILLA-) may be popular (-IN) (VILLAIN) and good for nothing (good-for-nothing = VILLAIN),
23 Second course (second ‘course’ = O-) with trimmed (c) piece of meat (‘cutlet’ without ‘c = -UTLET) (OUTLET) from market (OUTLET),
25 Airbrushes out Herb (‘airbrushes’ out/ without ‘Herb’ = airuss = RUSSIA) and Georgia’s neighbour (RUSSIA),
27 Some abandon a programme (some ‘abandon a programme’ = NAP) for break in the afternoon (NAP),
29 Fragment of Kashmir anecdote (some ‘Kashmir anecdote’ = IRAN) produced by Afghani neighbour (IRAN),
30 Supervisor cleans out pores (‘supervisor’ cleans out ‘pores’ = uvisr = VIRUS) – it might cause infection (VIRUS),
31 Spot (spot/pimple = BOIL) barrister (B-L) ringing to attract attention (oi! = -OI-) (BOIL),
34 Tear the (tear the = THEATRE) dress (= anagram indicator) in the gate (The Gate THEATRE)
35 Old agricultural worker (PEASANT) produced fuel (PEA-T) found over most of (d) the beach’s surface (‘sand’ without ‘d’ = -SAN-) (PEASANT),
36 Cryptic (SECRET) fan (ADMIRER) (SECRET ADMIRER) didn’t sign the Valentine’s Day card (SECRET ADMIRER).
Down:
2 Peer (equal) briefly (l) (‘equal’ without ‘l’ = EQUA-) takes to (-TO-) writing (from the 3Rs = -R) (EQUATOR) with a line that goes all the way around the world (EQUATOR),
3 Roulette ball limits (limits/sides of ‘roulette ball’ = ROLL) circular movement (ROLL),
4 Do one’s best (TRY-) gin (gin = -ING) cocktail (= anagram indicator) (TRYING) – it’s not easy (TRYING),
5 Make use of (EMPLOY) foreign (= anagram indicator) mole (mole = EM-LO-) over pressure (-P-) from Yard (-Y) (EMPLOY),
6 Vatican dismisses act (‘Vatican’ dismisses ‘act’ = vain = VAIN) as conceited (VAIN),
7 Guy (CHAP-) gets short (m) session (‘term’ without ‘m’ = -TER) (CHAPTER) on book contents (CHAPTER),
8 The Establishment (SOCIETY) is behind (= positional indicator) mystery (SECRET) (SECRET SOCIETY) of who organised the Easter Rising (SECRET SOCIETY),
9 “Privately, they elect political leaders (SECRET BALLOTS) with skeletons in the cupboards” (SECRET -S) – it’s all over introduction to Big (introduction to Big = B-) Issue (-ALLOT-) (SECRET BALLOTS),
14 Organisation (UN = NU-) digs up (= reversal indicator) definite (-CLEAR) (NUCLEAR)
type of energy (NUCLEAR energy)
16 Midwives (mid ‘wives’ = -V-) in new (= anagram indicator) role (role = LO-ER) (LOVER) similar to 18 down (LOVER is similar to ‘Venus’),
18 Most of (e) the stadium (‘venue’ without ‘e’ = VENU-) is sold initially (‘sold’ initially = -S) (VENUS) by Roman goddess (VENUS goddess of love),
20 De Niro isn’t part of rendition (‘De Niro’ isn’t part of ‘rendition’ = tin = NIT) from Dumbo (NIT),
21 Teacher (SIR) to Nicholas I responsible in part (‘Nicholas I responsible’ in part = SIR),
24 Bar for the swingers (TRAPEZE) in part (part = TRAP-) set up (= reversal indicator) with energy (-E-) and a fair amount of (half of) passion (half of ‘zeal’ = -ZE) (TRAPEZE),
26 Precious type (silver = -AG-) in repertoire (STOR-E) (STORAGE) has memory like a computer (STORAGE),
27 Splashed (= anagram indicator) scent – I (scent I = NICEST) find it most pleasant (NICEST),
28 All excited (PUMPED) as she avoided speed hump (‘she’ avoided/ is missing from ‘speed hump’ = pedump = PUMPED),
32 Some populist Iranians (some ‘populist Iranians’ = STIR) in mix (STIR),
33 Prepare to take flight (TAXI on runway) with what’s bound to concern revenue (what’s bound to concern Revenue = TAX-) from island (-I) (TAXI).