Across:
1 Weekend (‘weeK’ end = -K -) in revolutionary (= anagram indicator) Cuba (Cuba = BAC- U-) playing the lead (‘Playing’ the lead = -P) (BACK UP) or support? (BACK UP),
4 Upsets (= reversal indicator) English (-E) Fellow (man = NAM-) and most of the rest (most of the ‘rest’ = res = -SER) at university (U-) (USERNAME) with online identity (USERNAME),
9 Risk (CHANCE) of article (-AN-) dividing a number of religious institutions (Church = CH & Church of England = CE = CH-CE) (CHANCE),
10 Fundamental (ULTIMATE) sect (cult) loses leader (c) (‘cult’ without ‘c’ = ULT-) and one (-I-) confidante (-MATE) (ULTIMATE),
12 Ban (BAR-) footballer (-KEEPER) (BARKEEPER) who spends a lot of time in the New York pub (BARKEEPER),
13 It’s heart-warming without harming (‘heart-warming’ without ‘harming’ = etwar = WATER) what divides the Irish and the English (WATER),
14 Organised (= anagram indicator) races – the (the races = TEACHERS) step (step = PETS) up (= reversal indicator) (TEACHER’S PETS) for the classy favourites (TEACHER’S PETS),
18 Get to provide direction (CONTROL) on The Office’s (ROOMS) (CONTROL ROOMS) units keeping surveillance on the video feed (CONTROL ROOMS),
21 Grant (ALLOW) in Cork (Mallow) needs no introduction (m) (‘Mallow’ without ‘m’ = ALLOW),
22 Meet (ENCOUNTER) train (= anagram indicator) en route (en route = E- OUNTER) around North Carolina (-NC-) (ENCOUNTER),
24 A (A-) royal (-R-) soldier (-RANGER) (ARRANGER) presumably doing a blooming good job (flower ARRANGER),
25 Aspects (PHASES) of odd (= anagram indicator) shapes (shapes = PHASES),
26 Judge again (REASSESS) to study (read) briefly (d) (‘read’ without ‘d’ = REA-) ships (-SS-SS) on both sides of Spain (-E-) (REASSESS),
27 Picture (FRESCO) of sales force dumping ales (‘sales force’ dumping ‘ales’ = sforce = FRESCO).
Down:
1 Produce spiteful criticism (BACKBITE) of support (BACK-) for Sting (sting = -BITE) (BACKBITE),
2 Board member (CHAIRMAN) from Switzerland (CH-) is on the plane (-AIRMAN) (CHAIRMAN),
3 A French feminine type (French ‘a’ = une = UN-E) entertains 150 (Roman 150 = -CL-) (UNCLE) from the family (UNCLE),
5 Blame me (SELF-REPROACH) for narcissist’s obsession (SELF-) at work in the kitchen (prep) taking the head off (p) (‘prep’ without ‘p’ = -REP) fish (-ROACH) (SELF-REPROACH),
6 State (= homophone indicator) rule (‘reign’ = ‘rain’ = RAIN-) on 13 across (‘water’ = -WATER) (RAINWATER) and what’s in The Cloud presumably (RAINWATER),
7 Puts own stamp on (ADAPTS) fancy (= anagram indicator) tapas (tapas = A-APTS) around starter dish (starter ‘Dish’ = -D-) (ADAPTS),
8 Prayer meetings dismiss partying (‘prayer meetings’ dismiss ‘partying’ = ermees = EMEERS) by Arab rulers (EMEERS),
11 They’re perfect for those looking for an evening out (SPIRIT LEVELS) and the barman will be aware of them if he’s done a stocktake? (SPIRIT LEVELS),
15 Flips one’s lid perhaps (-WINKS) following (= position indicator) local tough (‘local’ tough = HOOD-) (HOODWINKS) fools (HOODWINKS),
16 Scot sent (scot sent = CONTESTS) off (= anagram indicator) in a number of competitions (CONTESTS),
17 Oriental (east = E-) state (= homophone indicator) plant (‘sow’ = ‘so’ = -S-O) admits pressure (-PRESS-) (ESPRESSO) can be stimulating (ESPRESSO),
19 Fundraiser (BAZAAR) on the radio? (= homophone indicator) Mystifying! (‘bizarre’ = ‘BAZAAR’)
20 Hear (= homophone indicator) him (‘him’ = ‘hymen’ = GLORIA) or is it her? (GLORIA),
23 Escort (USHER) is well (gusher) off from the start (g) (‘gusher’ without ‘g’ = USHER).