Across
1 subito S<(rurea)U/BIT>O
4 abacus A/B<A/C(helsea)>US
10 Amerindian A/MERI<N(orth)>DIAN
11 argyle ah! (hom) + guile (hom)
12 reediest IRE STEED (anag)
13,20 Year of the Rabbit (bab)Y<EAR/OF/THE/RABBI>(infan)T
15 icky (p)ICKY
16 tack double def
17,9 Watership Down WATERS<HIP>DOWN
21 dinosaur diner saw (hom)
22 replay REP/LAY
24 steel bands BLEND ASSET (anag)
25 twit T(o)/WIT
27,26 Warren Beatty BT (hom) on WARREN
Down
1 scourge S<CO(mpany)>URGE
2,5 bunny boiler BUN-NY + BOILER
3 tea leaf cryptic/rhyming slang
6 codpieces COD + PIECES
7 Starsky a hutch is smaller than a warren
8 search warrant WAR in NHS RAT RACE (anag)
14 rock opera PRE-COOK (anag) + (c)RA(b)
16 twin-tub WIN in BUTT (rev)
18 Eurasia U(zbecistan) in AREA IS (anag)
19 Italian (t)IT<ALI>AN
23 peter PETER (Rabbit) [peter out]