Across:
8 Immersed in Coup D’état, a nostalgic (immersed in ‘Coup D’étAT E NOStalgic’ = atanos) revolutionary (= reversal indicator) (atanos = SONATA) series of movements (SONATA),
9 Into the bargain (TOO-), lost (= anagram indicator) dole (dole = -DLE-O-) at job centre? (‘jOb’ centre = -O) (TOODLE-OO) That’s some parting shot! (TOODLE-OO),
10 In the bottleneck in the port (CORK) at the end of 13 down (end of ‘County Cork’ = CORK),
11 Throws down a gauntlet (CHALLENGES) to annoy (= anagram indicator) Hegel’s clan (Hegel’s clan = CHALLENGES),
12 Frenchman (Monsieur = M-) on course (-ASCOT racecourse) (MASCOT) has a reputation for being lucky with the followers (MASCOT),
14 Father (Da) sent back (= reversal indicator) (Da = AD-) to academy (Royal Irish Academy = -RIA-) – it’s an involuntary move (-TIC) (ADRIATIC) from part of the Med (ADRIATIC is part of the Mediterranean),
15 Most of those in 21 down (most of ‘issues’ = ISSUE) answer (answer = A) most of those in 11 across (most of ‘challenges’ = CHALLENGE) (ISSUE A CHALLENGE) with offer to invest in Donnybrook perhaps (invest in donnybrook/heated challenge = ISSUE A CHALLENGE),
18 Snaps (PICTURES) pie crust (pie crust = PICTURES) bake (= anagram indicator),
20 Nickel-and-dime linkmen missing (‘nickel-and-dime’ ‘linkmen’ missing = ceaddi = CADDIE) with bagman of course (CADDIE),
22 Is over the moon presumably (SPACECRAFT) with room (SPACE-) for art (-CRAFT) (SPACECRAFT),
24 Salt marsh banks (‘SAlt marSH’ banks = SASH) seen from the window (SASH window),
25 Workers (men) heading off (m) (‘men’ without ‘m’ = EN-) for what sounds like (= homophone indicator) days (‘days’ = ‘daze’ = -TRANCE) (ENTRANCE) to lobby (lobby/way in = ENTRANCE),
26 In retrospect (= reversal indicator), party (do = O-D) holding view (-EYE-) on first budget (first ‘Budget’ = -B-) (OBEYED) toed the line (OBEYED).
Down:
1 Noel Coward dismisses lewd (‘Noel Coward’ dismisses ‘lewd’ = nocoar = CORONA) section of The Sun (CORONA),
2 Lawmakers dismiss smear (‘lawmakers’ dismiss ‘smear’ = lawk = WALK) produced by tramp (WALK),
3 Can’t pet a (can’t pet a = PANCETTA) barking (= anagram indicator) type from butchers in Italy (PANCETTA),
4 No grain in Argentina (no ‘grain’ in ‘Argentina’ = enta = ETNA) or Sicilian hot spot (ETNA),
5 Can be raised to greet (BOWLER hat) and acknowledge applause (BOW-) opening laboratory (opening ‘Laboratory’ = -L-) in hospital (-ER) (BOWLER),
6 Put down one of those in the plot (PLANT A SEED) to create doubt (PLANT A SEED),
7 Standing in for (COVERING) what sounds like (= homophone indicator) Cobh (‘Cobh’ = ‘cove’ = COVE-) wedding band (-RING) (COVERING),
13 Down (COUNTY Down) and on the bottle (CORK) (COUNTY CORK) in Ireland (COUNTY CORK),
14 Perhaps a grateful (perhaps a grateful / grate full of ASHES) tout from south-east (‘tout’ from ‘south-east’ = sheas = ASHES),
16 Perform with a choir (S-ING) going around popular (-HIP-) port (-P-) (SHIPPING) or going through the Panama Canal, for example (SHIPPING),
17 Spot (LOCATION) line (L-) by Oscar (-O-) from action (action) novel (= anagram indicator) (action = -CATION) (LOCATION),
19 The latest (RECENT) recording equipment doing the rounds (‘RECording equipmENT’ doing the rounds = RECENT).
21 Broadcasts (ISSUES) to lots of children (ISSUES),
23 Exhibited the ravages of time (AGED) consumed by mortgage debt (consumed by ‘mortgAGE Debt’ = AGED),
24 Make out (SEE-) initial drummer (initial ‘Drummer’ = -D) (SEED) from Genesis (SEED).