Across:
1 Smack in the face (REBUFF) with cold shoulder (REBUFF),
4 They occupy (INVADERS) those who see The Border as something that can be overcome (INVADERS),
9 Constance has no son (‘Constance’ has no ‘son’ = ctance = ACCENT) for delivery, in a manner of speaking (ACCENT),
10 Cut top (s) herb (“sage” without “s” = AGE) bunch (GROUP) (AGE GROUP) from a similar vintage (AGE GROUP),
12 Couple of lines (-LL-) in Grease (smear = SME- A R-), the first (-A-) from the lead Travolta (lead ‘Travolta’ = -T) (SMELL A RAT), is suspect (SMELL A RAT),
13 Fight over (ARGUE) what’s hidden by unfamiliar guerrillas (ARGUE hidden by ‘unfamiliar guerrillas’),
14 Carol (S-ING) admits dance (-HOP-) and piano (-P-) record (LIST) (SHOPPING LIST) contains The Cranberries, Meatloaf and Red Hot Chili Peppers perhaps (SHOPPING LIST),
18 They pull the strings (PUPPET-MASTER) for the young wolf (PUP-), cat (-PET) and top dog (-MASTER) (PUPPET-MASTER),
21 Took steps (ACTED) to put on a show (ACTED),
22 Lough (Lough Ree = RE-E-) near French sea (French ‘sea’ = -MER-), for example (e.g. = -GE-), meanders around (= reversal indicator) Point (compass point south = -S) (RE-EMERGES) where it comes into view again (RE-EMERGES),
24 Criminal (CON-) lost partner (lost and -FOUND) (CONFOUND) in a maze? (amaze = CONFOUND),
25 Hark back to the time (RECALL) when there was no wine in wine cellar (no ‘wine’ in ‘wine cellar’ = cellar = RECALL),
26 Reduce speed, for instance (DECREASE), and speed camera will fail to get Pam (“speed camera” will fail to get/without “Pam” = seedcera = DECREASE),
27 Show up (ATTEND) to lure out of laundrette (‘lure’ out of ‘laundrette’ = andtte = ATTEND).
Down:
1 Consider in a different light (REASSESS) most of (l) the actual (“real” without “l” = REA-) engineering (-E-) found in two ships (SS-SS) (REASSESS),
2 Sounds like (= homophone indicator) Beany or Barney perhaps (Beany or Barney “Batchelors” peas and beans = one “batchelor” = “BACHELOR”) hasn’t got a regular mate (BACHELOR),
3 Some characters missing from Isle of Man (‘some’ characters missing from ‘Isle of Man’ = ilfan = FINAL) championship decider (FINAL),
5 PJ’s (NIGHTCLOTHES) employed to cover up those retiring (NIGHTCLOTHES),
6 It’s a feature of the Mediterranean (AEGEAN SEA) that this divides the Greeks and the Turks (AEGEAN SEA),
7 No huge (no huge = ENOUGH) problem (= anagram indicator) as there’s all you need (ENOUGH),
8 Small (S-) stimulant (-UPPER) (SUPPER) to swallow before bedtime (SUPPER),
11 Great (G-) African capital (African capital/money = -RAND) brings up (PARENTS) (GRANDPARENTS) kin from another generation (GRANDPARENTS),
15 Presumably in London this was the cost in hard cash (POUND NOTE) of hit (POUND) record? (NOTE) (POUND NOTE),
16 Don’t move (STAGNATE) from playground (play ground = STAG-E) around elevated (= reversal indicator) shade (tan = -NAT-) (STAGNATE),
17 Did a job in Ring (WRESTLED) with women (W-) to relax (-REST-) the foreign (the = -LE-) director (-D) (WRESTLED),
19 Had a ball perhaps (DANCED) in The Man (“Dan the man” = DAN-) from Clare (-CE-) with leading director (leading ‘director’ = -D) (DANCED),
20 The (the = ETH-) wrong (= anagram indicator) cut (nick) is trimmed (k) (‘nick’ without ‘k’ = ‘nic = -NIC) (ETHNIC) in one type of restaurant (ETHNIC restaurant),
23 Selectors to drop Ross (‘selectors’ to drop ‘Ross’ = elect = ELECT) or give him the seat? (ELECT).