Across:
1 Outlets (HO-SES) welcoming writing (from the 3Rs = -R-) (HORSE) by nags (HORSES),
4 American (A-) working in a restaurant (-WAITING) (AWAITING) is expecting (AWAITING),
9 Turns up (= reverse indicator), gangster (Don = N-OD) crosses river (-R-) near motorway (M1 = -IM-) (NIMROD) with hunter – that’s one for the books (NIMROD the Hunter in the Bible),
10 Bread (bread = TURNOVER) sales (TURNOVER),
12 Protested against (INVEIGHED) one (I-) given (given) collection (= anagram indicator) (given = -NVEIG-) by that man (-HE-) from department (-D) (INVEIGHED),
13 Broadcast (-ON-) by government (-G-) in California (CA = C-A) (CONGA) of party line? (CONGA line dance),
14 Shrewd bargaining (HORSE-TRADING) by most of those in 1 across (most of ‘horses’ = HORSE -) working in the city (working in The City = -TRADING) (HORSE-TRADING),
18 Off-putting (DISAGREEABLE) review of (= reversal indicator) papers (ID papers = DI-) finds fur coats (S-ABLE) okay (okay = -AGREE) (DISAGREEABLE),
21 Some deliver a token (some ‘delivER A TOken’ = ERATO) source of poetic inspiration (muse of lyrical poetry = ERATO),
22 Traditional (OLD SCHOOL) Platonic Academy (OLD SCHOOL),
24 Lock up (IMPRISON) in Portlaoise (Portlaoise -PRISON) behind (= position indicator) unit (I-) near motorway (-M-) (IMPRISON),
25 Supernaturalism disregards reprisals (‘supernaturalism’ disregards ‘reprisals’ = unatum = AUTUMN) when Halloween arrives (AUTUMN),
26 Show’s off (DISPLAYS) as director (D-) is (-IS-) at drama (-PLAY-) school (-S) (DISPLAYS),
27 A base (abase = DEMEAN) with terrain off Mediterranean (‘terrain’ off ‘Mediterranean’ = medean = DEMEAN).
Down:
1 Time to retire (NIGHT) after (= position indicator) foul (foul) broadcast (= homophone indicator) (‘foul’ = ‘fowl’ = HEN) (HEN NIGHT) of social that appeals to one joining a two-party system? (HEN NIGHT),
2 They’re capable of emptying The House (REMOVERS) for victor (-V-) in shocking (= anagram indicator) remorse (remorse = REMO-ERS) (REMOVERS),
3 Ran away from Caroline (‘ran’ away from ‘Caroline’ = colie = E COLI) producing a bad strain (E COLI),
5 Presumably, what The Lions are left with after getting beaten (WOUNDED PRIDE) is a slight to self-esteem? (WOUNDED PRIDE),
6 Clean hands (INNOCENCE) – you can’t be prosecuted for that! (INNOCENCE),
7 What the designer can do (INVENT) stems from investments (‘stems’ from ‘investments’ = invent = INVENT),
8 Frenchman (Monsieur = -M-) in Range (range) Rover (= anagram indicator) (range = GER-AN) (GERMAN) is heard travelling in parts of Austria (GERMAN),
11 Sounds like (= homophone indicator) scientific study of farming techniques (‘farmacology’ = ‘PHARMACOLOGY’) that might involve growing poppies? (PHARMACOLOGY),
15 The leader’s opinion (EDITORIAL), aside from the letter writers (EDITORIAL aside/at one side of “Letters to the Editor”),
16 Leo’s tuba (Leo’s tuba) played (= anagram indicator) (Leo’s tuba = ABSOLUTE) in total without qualification (ABSOLUTE),
17 Those providing cover for the King and Queen (BED LINEN) of Belgium (BE-) showing off (= anagram indicator) Linden (Linden = -D LINEN) (BED LINEN),
19 Stop (full stop = PERIOD) group of Seals (group of seals = pod = P-OD) holding back (= reverse indicator) resentment (ire = -ERI-) (PERIOD),
20 Travellers’ guide (map = PAM-) reviewed (= reverse indicator) with postscript (-P-S) about area (-A-) (PAMPAS) of flatlands around Buenos Aires (PAMPAS),
23 Creator (CAUSE) of Genesis? (CAUSE).