Across:
1 A French (a = UN-) sauce (sauce = -JUS-) for tempura starter (‘Tempura’ starter = -T) (UNJUST) isn’t right (UNJUST)
4 All back (= reverse all indicator) to go downhill (ski), mostly (i) (‘ski’ without ‘i’ = sk = -KS) with Síle (Sile = -ELIS-) and a fair amount of (half) boys (boys) (half of ‘BOys’ = bo = OB-) (OBELISKS), in columns (OBELISKS),
9 Instrument synonymous with Chippy (carpenter’s CHISEL) Carter is off the Richter Scale? (‘Carter’ is off the ‘Richter Scale’ = ihscle = CHISEL),
10 Unexpectedly (= anagram indicator) find Yeti (find Yeti = IDENTIFY) and give him a name (IDENTIFY),
12 Destabilise (UNBALANCE) one nice figure (one Nice/French figure/number: 1 = UN-) off set? (offset = -BALANCE) (UNBALANCE),
13 Clare (-CE-) is part of story (lie) told (= homophone indicator) (‘lie’ = ‘lye’ = LY-E) (LYCEE) to the French Institute (LYCEE / school),
14 Doesn’t come back with Sally (doesn’t come back with sally/attack = UNRESPONSIVE), and I’m keeping schtum (UNRESPONSIVE),
18 Organisation (UN-) at stable? (-DEPENDABLE) (UNDEPENDABLE) Certainly not the type you’d bet everything on! (UNDEPENDABLE),
21 Lawyer (Senior Counsel = SC-) for Band Aid (-AMP) (SCAMP) is a holy terror (SCAMP),
22 One (-I-) stuck in tight (= anagram indicator) entrance (entrance = NECTAR-NE) (NECTARINE) coming out of the orchard (NECTARINE),
24 Have just enough in one’s locker (SCRAPE BY) to beat (= anagram indicator) pacy Serb (pacy Serb = SCRAPE BY),
25 Hay from Himalayas (‘hay’ from ‘Himalayas’ = imlaas = SALAMI) or sausage from the deli? (SALAMI),
26 Sets up (= reverse indicator) Patsy (patsy/sap = PAS-) for scores on the rugby pitch (-TRIES) (PASTRIES) from a number of turnovers? (a number of turnovers = PASTRIES),
27 Shows contempt (SNEERS) for Head of State (head of ‘State’ = S-) backing (= reverse indicator) Partition (screen) without initial clue (‘initial Clue’ = ‘c’) (‘sCreen’ without ‘c’ = sreen = -NEERS) (SNEERS).
Down:
1 Uncut (uncut) version (= anagram indicator) (uncut = UNCTU-) out initially (‘Out’ initially = -O-) from America (-US) (UNCTUOUS) is excessively flattering (UNCTUOUS),
2 Robin (-BIRD) Mountjoy (Mountjoy JAIL-) is the first (= position indicator) (JAILBIRD local type having conviction (JAILBIRD),
3 Time (SPELL) to get all the characters in the right order (get all the characters/letters in the right order = SPELL),
5 Shift (BUDGE-) to Right is final (‘righT’ is final = -T) – talk (SPEECH) (BUDGET SPEECH) is, the Minister for Finance is responsible for it (BUDGET SPEECH),
6 Extended (LONG-) backing for (= reverse indicator) Old Nick (devil = LIVED) (LONG-LIVED) Hardy? (LONG-LIVED),
7 Barman (Senior Counsel = S-C-) protects funny fellow (-WIT-) from hotel (-H) (SWITCH) getting on (SWITCH on),
8 Designed (STYLED) eyesore (STY-) with one light (light-emitting diode = -LED) (STYLED),
11 A foreign (UN-) run (-GOVERN-) on banks? Abominable (banks ‘ABominabLE’ = -ABLE) (UNGOVERNABLE) and impossible to control! (UNGOVERNABLE),
15 Smooth (SANDPAPER) star (Star newspaper = -PAPER) on beach blanket (SAND-) from the start (= position indicator) (SANDPAPER),
16 Sailor (able-bodied seaman = AB-) taking LSD (acid) recalls (= reverse indicator) (acid = -DICA-) going around trial judge (going around ‘Trial judgE’ = -TE) (ABDICATE) to avoid ruling (ABDICATE),
17 Beef isn’t (beef isn’t) bad (= anagram indicator) (beef isn’t = BENEFITS) and does you good (BENEFITS),
19 Finishes the lot (USES UP) and takes drugs (USES) to stay awake (UP) (USES UP),
20 Crazy (MAD-) Irish race (Irish ‘race’ = rás = -RAS) (MADRAS) from old India (MADRAS),
23 Some of those put up (= reverse indicator) in Pennsylvania garret (put up in ‘pennsylvaNIA GArret’ = niaga = AGAIN) and not for the first time (AGAIN).