Across:
1 Social secretary loses royalties (‘social secretary’ loses ‘royalties’ = scaecr = SCARCE), in short (SCARCE),
4 They’ve no right to be in The House (BURGLARS) leading 11 down (leading ‘burglar alarm’ = BURGLAR-) for head of state (head of ‘State’ = -S) (BURGLARS),
9 Green olive gone off? (‘green olive’ ‘gone’ off/without ‘gone’ = relive = RELIVE) Go through again! (RELIVE),
10 Presumably, sent by a man of letters (EPISTLES) to run (= anagram indicator), sit, sleep (sit sleep = EPISTLES),
12 Built poor (built poor) structure (= anagram indicator) (built poor = POLITBURO) for The Party’s Committee (POLITBURO),
13 A wake-up call (ALARM) for those characters at the end of 11 down (at the end of ‘burglar alarm’ = ALARM),
14 Doesn’t forgive (BEARS A GRUDGE) 25 across opening (‘bear up’ opening = BEAR-) for South Africa (SA = -S A) and 19 down (‘grudge’ = GRUDGE) (BEARS A GRUDGE),
18 After trips perhaps, places where footballers get free shots (PENALTY SPOTS) – fine (PENALTY), if you have a rash? (SPOTS) (PENALTY SPOTS),
21 He got away from shooter (‘he’ got away from ‘shooter’ = sootr = ROOST) to settle down (ROOST),
22 American (A-) working on The Crown (dentist = -D-ENTIST) over Victor (-V-) (ADVENTIST) Christian (ADVENTIST),
24 Motivation (DRIVE-) for taking course of action (-WAY) (DRIVEWAY) – is that leading someone up the garden path? (DRIVEWAY),
25 Endure (BEAR UP) cutbacks (= reverse indicator)? Open account (open ‘Account’ = -A-) in Sterling (sterling/pure = -E-R UP) with British capital! (‘British’ capital = B-) (BEAR UP),
26 Let off (EXCUSE) for first murder? (first ‘Murder’ = M-) It’s an eye-opener (‘Eye’ opener = -E) (EXCUSE ME) begging your pardon! (EXCUSE ME!),
27 Give us a break (RECESS) in relation (RE-) to key (music key -C-) for fair (half) access (half ‘accESS’ = -ESS) (RECESS).
Down:
1 Have just enough in one’s locker (SCRAPE BY) to beat (= anagram indicator) pacy Serb (pacy Serb = SCRAPE BY),
2 Everyone (ALL) is plain to see (CLEAR) (ALL CLEAR) and you can’t get any better than that (ALL CLEAR),
3 Badly desire (COVET) something by the sea (COVE-) for the opening (‘The’ opening = -T) (COVET),
5 Useless (UNPRODUCTIVE) organisation (UN-) yielding results (-PRODUCTIVE) (UNPRODUCTIVE),
6 Estimates (GAUGES) behind (= position indicator) flag (sag) raised (= reverse indicator) (sag = GAS) (GAS GAUGES) in American vehicles providing an indication of energy levels (GAS GAUGES),
7 On the surface (AFLOAT), it’s for the St Patrick’s Day Parade (a float = AFLOAT),
8 Upsets (= reverse indicator) Eugene the First (‘Eugene’ the First = -E) at church service (Mass = S-SAM-) over closing quote (closing ‘quotE’ = -E) (SESAME) that could be the seed of something (SESAME seed),
11 By the sound of it, one primed to put gatecrashers off (BURGLAR ALARM) is a loud type doing security for The Doors (BURGLAR ALARM),
15 Small (-WEE-) South American accommodation (tepee = -T P-) found in bodies of salty water (seas = S- -EAS) (SWEET PEAS) with fragrant flowers (SWEET PEAS),
16 Relative (son) retires (= reverse indicator) (son = NO S-) to Ireland (-IRE-) from Spain? (-E) (NO SIREE) Dream on! (NO SIRREE),
17 One (I-) getting distress call (SOS = -SO-S) about Kitty (pot) picking up (= reverse indicator) (pot = -TOP-) energy (-E) (ISOTOPES) produced by radioactive type of elements (ISOTOPES),
19 Resentment (GRUDGE) looking back (= reverse indicator), for example (e.g. = G-E), over drug (drug = -RUDG-) boss (= anagram indicator) (GRUDGE),
20 Sets-up (= reversal indicator) firm (Co = O-C) incorporating assistance (aid = -DIA-) from foundation in Biarritz (foundation in ‘biarritZ’ = Z-) (ZODIAC) for those making predictions (ZODIAC),
23 Bottle containing Genie certainly (bottle containing ‘geNIE CErtainly’ = NIECE) produced by family member (NIECE).