Across:
1 Avoid (BYPASS) Trump ultimately (‘trumP’ ultimately = -P-) in abyss? (abyss) Wrong! (= anagram indicator) (abyss = BY-ASS) (BYPASS),
4 That’s embarrassing (ABASHING) for (A-) party (-BASH-) in (-IN-) Government (-G) (ABASHING),
9 One (I-) key (music key = -G-) for the gents (-LOOS) (IGLOOS) in blockhouses? (ice blocks for IGLOOS),
10 Working around The Courts (BALL BOYS working around the tennis courts), employed to pick up those getting hit hardest perhaps by The Rackets (BALL BOYS),
12 Senior (senior) boss (= anagram indicator) (senior = SERO-IN) hides Review (= reversal indicator) – not (not = -TON-) (SEROTONIN) that that might put you in a good mood (SEROTONIN)
13 Stewardess ignores stars (‘stewardess’ ignores ‘stars’ = ewdes = SWEDE) living in Europe (SWEDE),
14 Make Istanbul (make Istanbul) nervous (= anagram indicator) (make Istanbul = UNMISTAKABLE) beyond a doubt (UNMISTAKABLE),
18 Settled accounts (PAID THE PRICE) producing papers (-ID- papers) for trip he (trip he) made (= anagram indicator) (trip he = THE PRI-) in March (pace = PA- -CE) (PAID THE PRICE),
21 Set one’s heart on (CRAVE) enthusiastic praise (-RAVE) for college (C-) first (= position indicator) (CRAVE),
22 State (ANNOUNCE-) reception for head (‘Reception’ for head = -R) (ANNOUNCER) doing all the talking (ANNOUNCER),
24 Drunk in France (CALVADOS) gets locked first (‘locked’ first = -L-), tucking into Spanish wine (Cava = CA-VA-) at parties (dos = -DOS) (CALVADOS),
25 One is assisting the minister (CURATE) with review of (= reverse indicator) old separatist movement (ETA = -ATE) and old police force (Royal Ulster Constabulary = RUC = CUR-) (CURATE),
26 A (A-) partner (-MATE-) from Russia (RU) upsetting (= reverse indicator) (RU = -UR-) endless (end ‘lesS’ = -S) (AMATEURS) Corinthians (AMATEURS),
27 They’re on the house (tiles/SLATES) for classmate taking off Mac (‘classmate’ taking off / without ‘Mac’ = lasste = SLATES).
Down:
1 Barman (BL-) is (-IS-) going to party (Sinn Féin = -SF-) at university (University of Limerick = -UL) (BLISSFUL) in raptures (BLISSFUL),
2 It’s depressing (-GRIM-) in trip (slip) back (= reversal indicator) (slip = PI-LS) (PILGRIMS) with religious travellers (PILGRIMS),
3 Clamour (SHOUT) to transform (= anagram indicator) south (south = SHOUT),
5 Mind (BRAIN-) – this lot might have to be hung out to dry after this (-WASHING) (BRAINWASHING), as it’s part of the conditioning (BRAINWASHING),
6 Receipt (SALES SLIP) for some top (‘Some’ top = S-) beers (-ALES) and a fair amount of (half of) Pilsners knocked back (= reverse indicator) (half of ‘PILSners’ = pils = SLIP) (SALES SLIP),
7 Did some pressing work (IRONED) for Oscar (-O-) in new (= anagram indicator) diner (diner = IR-NED) (IRONED),
8 They’d make you laugh (gas men = GASMEN) in Government (G-) making up (= anagram indicator) names (names = -ASMEN) (GASMEN),
11 What an intern is expecting (UNPAID LABOUR) from organisation? (United Nations = UN-) Gainful employment! (-PAID LABOUR) (UNPAID LABOUR),
15 The draw (STALEMATE) of the French (‘the’ = -LE-) relative (-MA-) in France, for instance (state = STA-TE) (STALEMATE),
16 One of those on the runway (AIRCRAFT) to broadcast (AIR-) with one of those overseas (-CRAFT) (AIRCRAFT),
17 Musical talent (-EAR-) behind (= positional indicator) loud music (forte = F-) at takeaway (-LESS) (FEARLESS) is not afraid to have a go (FEARLESS),
19 A (A-) heartless (i) organisation of spies (CIA) (‘CIA’ without ‘I’ = -CA-) contacting agent’s (-CIA) (ACACIA) plant (ACACIA),
20 Foreign dish (PAELLA) in spring (leap) served up (= reverse indicator) (leap = PAEL-) with slaw (slaw), excluding the sides (‘s’ + ‘w’) (‘sLAw’ without ‘s’ + ‘w’= -LA) (PAELLA),
23 Stands up against leaders (‘Stands Up Against’ leaders = -SUA-) in university (University of Limerick = U-L) (USUAL) every day? (every day = everyday = USUAL).