Across:
1 Local rascal (SCAMP-) from institute (-I) (SCAMPI) produced something fishy (SCAMPI),
4 Ashley (-ASH) “Rocky” (= anagram indicator) Smith (smith = SM- HIT) is outside (SMASH HIT) at Number One presumably (SMASH HIT),
9 Genius (TALENT) old Roman capital? (old Roman capital/money coin = TALENT),
10 Takes a risk (STUNTMAN) falling for a star (STUNTMAN),
12 Grave type (SEPULCHRE) of dupes (dupes) losing the head (d) (‘dupes’ without ‘d’ = upes = SEPU-) over (= reversal indicator) long (-L-), heartless (o) chore (‘chore’ without ‘o’= -CHRE) (SEPULCHRE),
13 Container (CAN-) going back to Genoa (back to ‘Genoa’ = -A-) lost (-L) (CANAL) in Venice (CANAL),
14 Wrote about homes in conversation (= homophone indicator) (“homes” = “Holmes” – and DOCTOR WATSON is the narrator in the Sherlock Holmes stories) with fictional medic (DOCTOR WATSON),
18 Wine (wine = WE-IN-) made (= anagram indicator) around centre of Grand Duchy (centre of ‘Grand Duchy’ = -DD-) with top grapes (top ‘grapes’ =-G) is a demonstration (MARCH) (WEDDING MARCH) of what was noteworthy at the Marriage at Cana? (WEDDING MARCH),
21 Senate (HOUSE) is united (-U-) over pipeline (HO-SE) (HOUSE),
22 Runs home (HOUSEWIFE) from 21 across (‘house’ = HOUSE-) with mate (= WIFE) (HOUSEWIFE),
24 Whiskey (W-) sour (-OFF) arrives finally (= positional indicator) – service (-RITE) (WRITE-OFF) isn’t one to remember (WRITE-OFF),
25 The Star (SUN-) opens with 1 down (‘set-aside’ = -SET) (SUNSET) – at the end of the day you’ll only see that in The West (SUNSET),
26 Describe the spread of handy leaflets (leaves from a tree in the form of a spread hand = DIGITATE) of lady friend (date = D-ATE) welcoming single (-I-) leaders? Give it time! (leaders ‘give it time’ = -GIT-) (DIGITATE),
27 Relative (S-ON) admits former partner (-EX-) got time (-T-) (SEXTON) for burying people in the graveyard (SEXTON).
Down:
1 Place (SET-) on a (-A-) team (-SIDE) (SET-ASIDE) for reserve (SET-ASIDE),
2 Drunk (= anagram indicator) special (special = AL-SPICE) port (port/left = -L-) (ALLSPICE) with Jamaican seasoning (ALLSPICE),
3 Party all night at the summits (“party all night” at the summits/tops = PAN-) with the foreign (the = -EL) (PANEL) critics (PANEL),
5 Gucci, Gucci, Gucci – sounds like (= homophone indicator) something Mum said? (“Gucci, Gucci, Gucci” = “goochie, goochie, goochie” sounds like something Mum said = MOTHER TONGUE) All the babes out there understand that lingo! (MOTHER TONGUE),
6 Shock of speeding (shock wave travelling faster than the speed of sound = SONIC BOOM) with family member (SON-) – one (-I-) caught (-C-) in time just before a big crash (BOOM) (SONIC BOOM),
7 Set off something (‘set’ off ‘something’ = omhing = HOMING) for the pigeons? (HOMING pigeons),
8 Heartless (a) Harry (‘nag’ without ‘a’= -NG-) found in The Square on the ground level (tile = -TI-LE) (TINGLE) sends a shiver down one’s spine (TINGLE),
11 Had words with (CHEWED THE FAT) 19 down (‘chewed’ = CHEWED) over (= anagram indicator) a theft (a theft = THE FAT) (CHEWED THE FAT),
15 Finished (OVER-) with struggle in Labour (-EXERT) (OVEREXERT), as it sounds like it’s too much work (OVEREXERT),
16 Coach (TRAIN) park (SET) (TRAIN SET) is a childish option for the present (TRAIN SET),
17 Strike possibility (THREATEN strike) put at risk (THREATEN),
19 Had the bit between one’s teeth (CHEWED) as revolutionary (CHE-) got married (-WED) (CHEWED),
20 Pulling a face (pouting) off the top (p) of one’s head (p) (‘pouting’ without ‘p’ = OUTING) can be revealing (OUTING),
23 It’ll come out (EXUDE), old partner (EX-) is due (due = -UDE) treatment (= anagram indicator) (EXUDE).