Across:
1 Greatest footballer (George B-EST) grabs a (-A-) shirt at the top (‘Shirt’ at the top = -S-) (BASEST) – it’s most improper (BASEST),
4 What the musicians produced (THE BLUES) in period of Depression? (THE BLUES),
9 Speaks volumes perhaps (ORATOR) turning up (= reverse indicator) for work schedule (rota = -ATOR) with reduced (d) staff (rod) (‘rod’ without ‘d’ = ro = OR-) (ORATOR),
10 Producer (maker = MA- -KER) rings UK leader (Prime Minister = -P M-) and American leader (‘American’ leader = -A-) (MAP MAKER) sketching out how the world looks (MAP MAKER),
12 What you might do with an abacus (COUNT ON IT)? Absolutely! (COUNT ON IT),
13 Taste (SENSE) sample of delicatessen seasonings (sample of ‘delicatesSEN SEasonings’ = SENSE),
14 Learnt one’s own lessons, of course (SELF-EDUCATED), by opening 18 across (opening ‘self-employed = SELF -) with dead cute (dead cute) cook (= anagram indicator) (dead cute = EDUCATED) (SELF-EDUCATED),
18 Has a job minding one’s own business (SELF-EMPLOYED) in Labour – for one, not being part of the general staff (SELF-EMPLOYED)
21 Pull (CLOUT) opening commentary (opening ‘Commentary’ = C-) from Yahoo (yahoo/thug = -LOUT) (CLOUT),
22 Is friendly (CONVIVIAL) with Sting (CON-) at 6 (-VI-) 6 (-VI-)? Sending up (= reverse indicator) The French! (‘the’ French = la = -AL) (CONVIVIAL),
24 Pulls the plug on (DISABLES) short (c) basic (basic) rebellion (reverse indicator) (‘basic’ without ‘c’ = basi = -ISAB-) in Donegal (DL = D-L-) by early seditious leaders (‘Early Seditious’ leaders =-ES) (DISABLES),
25 Fly (CADDIS fly) to California (CA-) from Dublin (-D-) with a fair amount of (half) dismay (half of ‘DISmay’ = -DIS) (CADDIS),
26 They have new faith (CONVERTS) in priest (Rev) over (= reverse indicator) (Rev = -VER-) time (-T-) welcomed by inmates (cons = CON-S) (CONVERTS),
27 Riga abandoned by brigadiers (‘Riga’ abandoned by/ out of ‘brigadiers’ = bdiers = DEBRIS) in ruins (DEBRIS),
Down:
1 Cabinet (BOOKCASE) order (order/reserve = BOOK-) comes in front of the judge (-CASE) (BOOKCASE),
2 Drunk (= anagram indicator) slugs ale (slugs ale = SEAGULLS) with the birds in The Marina (SEAGULLS),
3 Clamour (SHOUT) to transform (= anagram indicator) south (south = SHOUT),
5 Central (HEART-) heating (-WARMING) (HEART-WARMING) is gratifying (HEART-WARMING),
6 This will come as a shock (BOMBSHELL), as it’s in The Magazine (find BOMBSHELL in the magazine / ammunition store),
7 It’s not Nice at all (not nice at all = UNKIND) for a French (‘a’ French = UN-) family (-KIN-) from 6th Arrondissement (6th letter of “arronDissement” = -D) (UNKIND),
8 Turns up (= reversal indicator), left (-L) lover (Greek god of love = Eros = -SO-RE-) over race tip (‘Race’ tip = -R-) (SORREL) for horse (SORREL),
11 Popular (IN-) enough (-SUFFICIENT) (INSUFFICIENT), as it’s in short supply (INSUFFICIENT),
15 The Spanish (‘the’ Spanish = EL-) community (European Community = -EC-) club for swingers (cub/bat for swinging batsman = bat) set-up (= reverse indicator) (bat = -TAB-) by The French (‘the’ French = -LE) (ELECTABLE) is a good candidate for success (ELECTABLE),
16 Ned Cyril (Ned Cyril) Rock (= anagram indicator) (Ned Cyril = CYLINDER) is a solid rotund figure (CYLINDER),
17 Admires (IDOLISES) one (I-) party (-DO-) on Isle (Isle) angry (= anagram indicator) (Isle = -LISE-) with head of state (head of ‘State’ = -S) (IDOLISES),
19 Is bitter (ACIDIC) with accountant (CA) over (= reverse indicator) (CA = AC-) the papers (-ID- papers) getting one (-I-) caught (-C) (ACIDIC),
20 No interest in neuroscientist (no ‘interest’ in ‘neuroscientist’ = uocnis = COUSIN) – a member of the extended family (COUSIN),
23 In a frenzy (IRATE), buccaneer (pirate) loses the head (p) (‘pirate’ loses ‘p’ = IRATE).