Across:
1 Old (O-) tape (tape) playing (= anagram indicator) (tape = -P-ATE) contains single (-I-) (OPIATE) produced by The Chemical Brothers perhaps (OPIATE),
4 Go overseas (SWIM-) for legal action (-SUIT) (SWIMSUIT) covering beach bum? (SWIMSUIT),
9 Primate leaves prayer meeting (‘primate’ leaves ‘prayer meeting’ = yereng = ENERGY) with enthusiasm (ENERGY),
10 Finish work (KNOCK-OFF) in Mayo (KNOCK) and go on holiday (on holiday = OFF) (KNOCK-OFF),
12 Worry (care = CA-RE) about key (music key = -F-) English (-E-) chain (-TIE-) (CAFETIERE) making hot drinks (CAFETIERE),
13 English (E-) Times (times/multiplication symbol = -X-) has leaderless (f) column (column/row = ‘file’ without ‘f’ = -ILE) (EXILE) with a sentence that’s obviously political (EXILE / deport is a political sentence/punishment),
14 Those involved in court proceedings (MIXED DOUBLES on tennis courts) produced a range of large cocktails with a number of spirits (MIXED DOUBLES),
18 Sweet (DESSERT-) starters sold primarily out of necessity (starters ‘Sold Primarily Out Of Necessity’ = -SPOON) (DESSERTSPOON) in the canteen (DESSERTSPOON),
21 Unfinished (e) Dublin hospital (Coombe Hospital, Dublin) (‘Coombe’ without ‘e’ = COOMB) in the valley close to The Hill? (COOMB),
22 About (RE-) to join model (-EXHIBIT) (RE-EXHIBIT) put out by the curators again (RE-EXHIBIT),
24 10,9,8,7,6,5,4,3,2,1 (numbers go from ‘10’ to ‘1’ = TEN TO ONE) = 1,250? (12.50pm = TEN TO ONE),
25 A general rule (canon = CAN-ON) covering new (-N-) (CANNON) equipment produced by a major employer (CANNON produced by major employer/army),
26 Head barman (Attorney General = AG = A G-) opening for office (opening for ‘Office’ = -O-) party (do) returning (= reverse indicator) (do = -OD) back (BET) (A GOOD BET) from 24 across, for example, only if it’s worth the risk (for example, odds of ‘ten to one’ are A GOOD BET is the risk pays off),
27 Take another cut (RE-EDIT) out of desperate (= anagram indicator) dieter (dieter = RE-EDIT).
Down:
1 Master (OVERCOME) is speechless (OVERCOME),
2 Sets-up (= reversal indicator) old partner (ex = -XE) with one (-I-) means of broadcasting (feed = -DEE F-) from island (I-) (IDÉE FIXE) – it’s an obsession (IDÉE FIXE),
3 Local drunk (TIGHT) has a habit of going missing when it’s his round presumably (TIGHT),
5 Season (WINTER) for making beer (BARLEY) (WINTER BARLEY) and feeding animals (WINTER BARLEY),
6 Relative (MA-) caught (-C-) with the most important parts of something (kernels) gutted (n) (‘kerNels’ missing ‘n’ = KERELS) (MACKERELS) in fish? (MACKERELS),
7 Outs a pilot not getting lots (‘outs a pilot’ not getting ‘lots’ = ‘outapi’ = UTOPIA) of more work? (Thomas More’s UTOPIA),
8 Fudge (TOFFEE) by old (-O-) party (Fianna Fáil = -FF-) consumed by golf supporter, of course? (tee = T-EE) (TOFFEE),
11 Unstable (= anagram indicator) Roman centres (Roman centres = REMONSTRANCE) of protest (REMONSTRANCE),
15 Produced sketches (DREW) for The Family (BLOOD) (DREW BLOOD) – is that what the count did? (Count Dracula DREW BLOOD?),
16 Got together (COMBINED) to search everywhere (COMB-ED) around at home (-IN-) (COMBINED),
17 Has natural ability (INSTINCT) to nose? (INSTINCT),
19 Local diamonds (‘diamonds’ locally = ICE) sourced from China originally (TEA) (ICE TEA) by cool type during the summer (ICE TEA),
20 Delivered (BORN-) by middle of September (middle of ‘septEmber’ = -E-), order (-O) (BORNEO) to a primitive lad’s home perhaps (BORNEO)
23 Clip (n) of Nirvana (‘heaven’ without ‘n’ = HEAVE) in lift? (HEAVE).