Across:
8 Do come off main road (‘do’ come off ‘main road’ = mainra = MARINA) for harbour (MARINA),
9 Left on The Helga? (left on The Helga/ship = PORT-) Leaders with Irish commanding officer see (leaders with ‘Irish commanding officer see’ = ICOS) (PORTICOS) them in front of GPO and other church buildings! (PORTICOS),
10 Dust (DIRT) picked up (= reversal indicator) in cartridges (in ‘cartridges’= trid = DIRT),
11 It’s pretty (DELIGHTFUL) beautiful (DELIGHTFUL),
12 Accountant (CA-) on board (steamship = -SS-) returns (= reversal indicator) first class (AI = IA = -IA) (CASSIA) with Senna (CASSIA tree),
14 Everyone (ALL-) is plain to see (-CLEAR) (ALL CLEAR) and you can’t get any better than that (ALL CLEAR),
15 Arrange (SETTLE) ancient (OLD) types of music (SCORES) (SETTLE OLD SCORES) produced to get revenge (SETTLE OLD SCORES),
18 Funny (HUMOROUS) organic matter (humus = HUM-US) found around summits with old rocky outcrops (summits with ‘old rocky outcrops’ = -ORO-) (HUMOROUS),
20 Made a home (NESTED) out of necessity (NE-ED) across the street (-ST-) (NESTED),
22 Ran out of type of words (SPEECHLESS) for form of delivery one might get (SPEECH-) from Takeaway (take away = -LESS) (SPEECHLESS),
24 Rome, for one (CITY), and Milan sacked by militancy (‘Milan’ sacked by/ taken from ‘militancy’ = itcy = CITY),
25 Drunk (= anagram indicator) slugs ale (slugs ale = SEAGULLS) with the birds in The Marina (SEAGULLS),
26 Puts up (ERECTS) secret (secret = ERECTS) organisation (= anagram indicator).
Down:
1 Starts for a job in Tipperary area (starts ‘for a job in Tipperary area’ = FAJITA) advertised in Tex-Mex restaurant (FAJITA),
2 Let it be known indirectly (HINT) there are no wagons in Washington (no ‘wagons’ in ‘Washington’ = hint = HINT),
3 The Queen (CARD) is match (GAME) (CARD GAME) for old maid (Old Maid = CARD GAME),
4 Reveal a policy covering up (‘reveal a policy’ covering up = lapo = OPAL) review (= reversal indicator) by one of The Stones (OPAL),
5 Withhold tune from Ungrateful (withhold ‘tune’ from ‘ungrateful’ = ugrafl = FRUGAL) Dead – mean that is! (dead mean that is = FRUGAL),
6 10 across (‘dirt’ = DIRT-) from Yard (-Y) searches (LOOKS) (DIRTY LOOKS) for daggers? (DIRTY LOOKS),
7 Loud mate (loud mate = MODULATE) freaks out (= anagram indicator) in temper (MODULATE),
13 Irritates (SETS ON EDGE) determined (SET-) relative (son = -S ON) at Fringe (EDGE) (SETS ON EDGE),
14 Greek taken out of Great Lakes (‘Greek’ taken out of ‘Great Lakes’ = atlas = ATLAS) has a lot on his shoulders (in mythology, ATLAS has the weight of the world on his shoulders),
16 Provided for (EQUIPPED) Sally (-QUIP-) in deep (deep = E-PED) trouble (= anagram indicator) (EQUIPPED),
17 Sister (Sr = S-R) gets on (gets on = -ONGSTE-) badly (= anagram indicator) inside (SONGSTER) with diva (SONGSTER),
19 Waiting to talk (ON HOLD) to switch (ON) for support (HOLD) (ON HOLD),
21 Literary agent disregards a larger (‘literary agent’ disregards ‘a larger’ = iteynt = ENTITY) organisation (ENTITY),
23 It’s not difficult (EASY) for Ken to leave Yankees (‘Ken’ to leave ‘Yankees’ = yaes = EASY),
24 Banks credit review (banks/sides ‘credit review’ = CREW) of ship’s company (CREW).