Across:
1 Forge (SMITHY) crazy (= anagram indicator) myths (myths = SM-THY) about island (-I-) (SMITHY),
4 Leader of Band (leader of ‘Band’ = B-) Aid’s (aids = -ASSISTS) (BASSISTS) musicians (BASSISTS),
9 Ban (OUTLAW) leads, ores, uranium, titanium (leads ‘Ores Uranium Titanium’ = OUT-) with legislation (-LAW) (OUTLAW),
10 Is capable of holding one’s beer (SCHOONER glass) leaving The Marina perhaps (SCHOONER),
12 Tom’s rogue (Tom’s rogue) design (= anagram indicator) (Tom’s rogue = GUESTROOM) has a space for drop-ins (GUESTROOM),
13 Some get along (some ‘geT ALONg’ = TALON) with grabber associated with high-flyer (TALON),
14 Most important position for The Lions (PRIDE OF PLACE) in 23 down (‘pride’ = PRIDE)? For Old French (Old French = OF) it’s nearly all those (most of) in 20 down (most of ‘places’ = PLACE)! (PRIDE OF PLACE),
18 3 down (‘heart’ = HEART-) and 8 down (‘string’ = -STRING-) on last chances (last ‘chanceS’ = -S) (HEARTSTRINGS) with those who can be tugged emotionally (HEARTSTRINGS),
21 Broadcast (RELAY) with electrical device (RELAY),
22 Timeless (ATEMPORAL) area (A-) and square (T- square) near Palermo (Palermo) ruins (= anagram indicator) (Palermo = -EMPORAL) (ATEMPORAL),
24 Champ (VICTOR-) starters in Adelaide (starters ‘In Adelaide’ = -IA) (VICTORIA) produced in Australia (VICTORIA),
25 Mark (SIGN-) English (-E-) is ahead of Troy (a head of ‘Troy’ = -T) (SIGNET) Ring (SIGNET ring),
26 Testing (ASSAYING) a (A-) small (-S-) saw (saw/proverb = -SAYING)? (ASSAYING),
27 Guard (DEFEND) is fed (fed) up (= reverse indicator) (fed = DEF-) with wind up (wind up = -END) (DEFEND).
Down:
1 In a roundabout way (= reversal indicator), spring (spa = -APS) is great (-G-) for containers (pots = STOP-) (STOPGAPS), as they're only temporary measures (STOPGAPS),
2 One (I-) Pinter (Pinter) play (= anagram indicator) (Pinter = -NTREPI-) directed (-D) (INTREPID) by fearless type (INTREPID),
3 Pick up (HEAR-) car (model T = -T) (HEART) with enthusiasm (HEART),
5 Expert in the field (ACCOMPLISHED) produced (= anagram indicator) chemical pods (chemical pods = ACCOMPLISHED),
6 Lasting impression (scar = S- CAR) going around harbours (-PORTS) (SPORTS CAR) in fast vehicle (SPORTS CAR),
7 Only one (SINGLE) hour (h) from Pebble Beach (‘shingle’ without ‘h’ = SINGLE),
8 Street (ST-) in Waterford (-RING) (STRING) with a group of Arabians? (STRING of horses/Arabians),
11 Verification (CONFIRMATION) in the past, one would have got a slap for this (CONFIRMATION),
15 They are all (EVERYBODY) offering sea view alternatively (‘sEa ViEw’ alternatively/ alternative letters = EVE-) with right of way on the outskirts (‘Right of waY’ on the outskirts = -RY) for soulmate (-BODY and soul) (EVERYBODY),
16 Workers (men) heading off (m) (‘men’ without ‘m’ = EN-) for what sounds like (= homophone indicator) days (‘days’ = ‘daze’ = -TRANCE) (ENTRANCE) to lobby (lobby/way in = ENTRANCE),
17 One (I-) criticised harshly (slated = -S-LATED) over nothing (-O-) (ISOLATED) is hard to find (ISOLATED),
19 Log in leaving invigilator (‘log in’ leaving ‘invigilator’ = iviatr = TRIVIA) the unimportant facts (TRIVIA),
20 Puts one’s fingers on (PLACES) what’s said to be (= homophone indicator) fish (‘plaice’ = ‘place’ = PLACE-) sauce, for starter (‘Sauce’ for starter = -S) (PLACES),
23 Cats from pit scared (‘cats’ from ‘pit scared’ = pired = PRIDE) by a group of ferocious animals (PRIDE).