Across:
8 Immersed in Coup D’état, a nostalgic (immersed in ‘Coup D’état a nostalgic’ = atanos) revolutionary (= reversal indicator) (atanos = SONATA) series of movements (SONATA),
9 Paint a picture of (DESCRIBE) date (D-) with English (-E-) writer (-SCRIBE) (DESCRIBE),
10 Opens 15 across (opens ‘mark the occasion’ = MARK) in old capital (old capital/money = MARK),
11 Garda’s (Gardas = DIs = DIS-) union (-HARMONY) (DISHARMONY) produced conflict (DISHARMONY),
12 Fear (PHOBIA) of copper (penny = P-) finding what’s illegally obtained (hot) mostly (t) (“hot” without “t” = -HO-) from bank (AIB) hold-up (= reversal indicator) (AIB = -BIA) (PHOBIA),
14 Be unsure (HESITATE) that man (HE-) is (is) retiring (= reversal indicator) (is = -SI-) from foreign museum (-TATE) (HESITATE),
15 Kay (-K) Sully (sully = MAR-) provides the introduction (= positional indicator) and most (m) of them (‘them’ without ‘m’ = THE) do (OCCASION) (MARK THE OCCASION) raise a glass (MARK THE OCCASION),
18 One (I-) sought office (-RAN-) for half the Italians (half the ‘Italians’ = -IANS) (IRANIANS) in 5 down, for instance (“Asians” = IRANIANS),
20 Views (VISTAS) of movie stars missing Rome (‘movie stars’ missing ‘Rome’ = vistas = VISTAS),
22 Has no chance of success (NON-STARTER) staying at The Post? (staying at the post in racing = NON-STARTER),
24 Fragment of sci-fi legacy (fragment of ‘sci-fi legacy’ = FILE) produced by partner of Rank (rank and FILE),
25 Fellow (ACADEMIC) produced a (A-) computer-aided design (computer-aided design = -CAD-) to train (= anagram indicator) mice (mice = -EMIC) (ACADEMIC),
26 Drop (PLUNGE) pressure (P-) from spring (-LUNGE) (PLUNGE).
Down:
1 Drugs (POT-) for scratching the head (r), irritating skin problem (‘rash’ without ‘r’ = -ASH) POTASH) and increasing fertility (POTASH fertiliser),
2 Muck around (LARK) on the banks to lay the groundwork (on the banks to ‘lay the groundwork’ = LARK),
3 It’s difficult (HARD) to get top Christmas (top ‘Christmas’ = C-) Tree (-ASH) (HARD CASH) with the pocket money that’s available? (HARD CASH),
4 Leaderless (s) factions (‘sides’ without ‘s’ = IDES) in Rome warned about them (IDES of March warning to Caesar),
5 Absent from San Sebastian (‘absent’ from ‘San Sebastian’ = snasia = ASIANS) and from Tokyo (ASIANS),
6 Prepares for the stage (DRAMATISES), funny (= anagram indicator) mad satires (mad satires = DRAMATISES),
7 Last of the data (last of the ‘data’ = A-) conceals the dirt (bin = -B IN) in the interests of leaders (‘in the interests of’ leaders = ITIO) (AB INITIO) in Latin countries to begin with (AB INITIO),
13 Graduate (BA-) from The Palace (-KING) on the drink (SODA) (BAKING SODA) with agent responsible for The Rising (BAKING SODA),
14 Dances (HOOFS) to loud music (forte = -F-) in Soho (Soho = HOO-S) medley (= anagram indicator) (HOOFS),
16 A (A-) female (F-) in Corrie (Corrie = IR -ORCE) playing (= anagram indicator) (AIR FORCE) one of the high flyers (AIR FORCE),
17 They hide what’s really happening (COVER-UPS) from mugs (C-UPS) boxing – it’s no longer on (-OVER-) (COVER-UPS),
19 Hair-raising moments (ALARMS) for air marshal with no hair? (‘air marshal’ with no ‘hair’ = amarsl = ALARMS),
21 Bear witness to (ALLEGE) sons from Los Angeles (‘sons’ from ‘Los Angeles’ = lagele= ALLEGE),
23 Credit local (TICK) with some trademark citation (some ‘trademark citation’ = kcit) to back it up (= reversal indicator) (kcit = TICK),
24 It’s distasteful (FOUL) to offend (‘off’ end = F-) Oxford (-O-) College (University of Limerick = -UL) (FOUL).