Solving time, 19 mins
* = anagram < = reversed
ACROSS
8 LAP IDA TED pal<
Archaic word meaning ‘pelted with stones’ that I worked out from the wordplay, verifying after.
9 D(rum)ROLL Again worked it out from the clue, and then verified that Haydn did indeed compose a Drum-Roll Symphony
10 OARSMAN (On Mars a)*
11 CAST(OR)S
12 ID EST Hidden
14 CLAM OUR ED My favourite clue
15 GIVE ONESELF AWAY
19 FU (RN I) TURE My last entry.
21 TR END Rt<
23 AR (A L S) EA
24 GENT EEL
26 C (HIM)E
27 OSTENSIVE (Eve isn’t so)* A fairly obvious anagram for a word that was new to me.
DOWN
1 A LL OWING Liked this
2 SPUR GE (e.g.)<
3 EDAM made< &lit, I guess
4 A TONIC
5 I DE CLARE
6 TOM (s)ORROW
7 C (LOSE)D
9 DISCO M FIT
13 TOOK ISSUE Double definition
16 VERBATIM (Ambivert)*
17 E DUCAT OR
18 Y (OD) ELLED do<
19 FIANCE i for r in France
20 (w)EIGHTY
22 EM ETIC (cite me)<
25 NENE Double definition It’s an English river so the English is not equal to E here.