Across:
1 Add colour to the material (TIE-DYE) that is (i.e. = -IE-) consumed by politician (TD = T-D-) – for sure (yes) it’s not finished (s) (‘yes’ without ‘s’ = -YE) (TIE-DYE),
4 Without a joint (SEAMLESS), it won’t have you in stitches (SEAMLESS).
9 Broadcast (AIR) most (k) of the slimy stuff locally (gunk) (‘gunk’ locally = GUN) (AIR GUN) that’s used to get rid of vermin (AIR GUN),
10 There’s no end to this (ETERNITY) entire (entire) melody (= anagram indicator) (entire = ETERNI-) by The Yardbirds, for starters (‘The Yardbirds’ for starters = -TY) (ETERNITY),
12 Style of jazz (SWING) heard in the house (VOTE heard in The House/Dáil) (SWING VOTE) produced by a select crowd that can go either way? (SWING VOTE),
13 Ulster (-NI-) approaching top out-half (top ‘Out-half’ = -O-) in a French (‘a’ French = un = U-N) (UNION) club (UNION),
14 Enthusiasm (PASSION) for the pair (pair) on the radio (= homophone indicator) (‘pair’ = ‘pear’ = FRUIT) (PASSION FRUIT) grows in tropical areas (PASSION FRUIT),
18 We Irish owe all of this (NATIONAL DEBT) to citizen (NATIONAL) setting up (= reverse indicator) Foundation (bed = DEB-) on time (-T) (NATIONAL DEBT),
21 Cover story (ALIBI) of some Somali bishop (some ‘somALI BIshop’ = ALIBI),
22 Use the last of (‘use’ the last of = E-) rotten (anagram indicator) manure (manure = -NUMERA-) on a fair amount of (half of) the site (half of ‘siTE’ = -TE) (ENUMERATE) for Count (ENUMERATE),
24 Sets up (= reverse indicator) sailor (able-bodied seaman = AB = -BA-) bar (inn = -NNI-) in American city (LA = -A-L) with first cousin (first ‘Cousin’ = C-) (CANNIBAL) – a man-eater (CANNIBAL),
25 Forerunner to CAB (forerunner to cab/taxi = HANSOM) in attractive (handsome) state (= homophone indicator) (‘handsome’ = ‘HANSOM’),
26 Telegraph’s (telegraphs/sends = S-ENDS) covering of unique selling point (Unique Selling Point = = -USP-) (SUSPENDS) of swings (SUSPENDS),
27 Soldier (GI = G-I-) over first lieutenant (first ‘Lieutenant’ = -L-) on the German (‘the’ German =-DER) (GLIDER) aircraft (GLIDER).
Down:
1 Strange (= anagram indicator) patterns (patterns = TRANSEPT) found in the chapel (TRANSEPT),
2 First (EARLIEST) Oriental (East = E-) myths (-LIES-) discovered in contents of museum (art = -AR-T) (EARLIEST),
3 It’s juvenile (YOUNG) to open 11 down (open ‘young Ireland’ = YOUNG),
5 Big shot (ENTREPRENEUR) produced The Hustler (ENTREPRENEUR),
6 Temperamental (MERCURIAL) workers (men) for the most part (n) (‘men’ without ‘n’ = ME-) at court (Curia Papal Court = -CURIA-) in Lebanon (RL = -R-L) (MERCURIAL),
7 Turns up (= reversal indicator) bug (rile = EL-IR) catches one (-I-) mystery man (-X-) (ELIXIR) offering magic potion (ELIXIR),
8 Easy going, lacking ego (‘easy going’, lacking ‘ego’ = asying = SAYING) and getting opinions across (SAYING),
11 Type of litter (YOUNG) found on this island (IRELAND) (YOUNG IRELAND) produced by old social and political movement (YOUNG IRELAND),
15 Leans over in stressful way when making a note (ITALICISE) of the greatest (Muhammad Ali = -ALI-) in foreign (= anagram indicator) cities (cities = IT-CIS E) (ITALICISE),
16 Small (-S-) friend (pal) trips up (= reversal indicator) (pal = -LAP-) in grass (RE-ED) (RELAPSED) and got sick again (RELAPSED),
17 Flag (STREAMER) from wild (= anagram indicator) tree’s arm (trees arm = STREAMER),
19 Accountant (CA-) heads for Uruguay, Colombia (heads for ‘Uruguay, Colombia’ = -UC-) and America (-US) (CAUCUS) from political meeting (CAUCUS)
20 Must get away from the assumption (‘must’ get away from the ‘assumption’ = aspion = PIANOS) these are for key players? (PIANOS),
23 One may have an attachment (EMAIL may have an attachment) to picking up (= reverse indicator) William (Liam = -MAIL) Blake’s last letter? (Blake’s last letter/last letter of ‘blakE’ = E-) (EMAIL).