The leader board would suggest that this was not as tough as I made it in my 28 minutes of struggle, and I can’t really claim that I took it steady so as to parse everything. I didn’t. I did have a few misgivings over some of the definitions, though, which should be apparent from the remarks below.
A curiosity of this one is the (probably record) number of clues which depend on the Nato alphabet.
I retain my practice of highlighting clues, definitions and SOLUTIONS
1 Very alcoholic party — something served in the can? (4,6)
HARD LABOUR So: very alcoholic is HARD (as in liquor) and party is LABOUR, and the definition is a cryptic reference to an enhancement of punishment in prison (slang: can) still practiced in surprisingly many nations.
6 Damage appeal when caryatid’s head is knocked off (4)
HARM Appeal is CHARM, remove the Caryatid’s head. You don’t need to know what a caryatid is.
9 Playmates upset about fine for something that was found in pit (6,4)
SAFETY LAMP Humphrey Davy’s life saving invention derived for us from the letters of PLAYMATES “upset” and F(ine)
10 Excellent American taking no exercise is feeling pain (4)
ACHY Ah yes, this is PEACHY (not only) American for excellent, with its PE (exercise) removed
12 Meeting in brief before court case that’s not begun (12)
INTERSECTION In: IN, brief: TERSE, court case ACTION, remove the first letter
15 Pochard is flying high (9)
RHAPSODIC The appropriate definition from Chambers is (of) an ecstatic utterance of feeling so “high” clings to that. The wordplay looks like an anagram, and is (flying) of POCHARD IS
17 Axis spy? No? Yes — German, not English (5)
NINJA So... the wordplay allows us to resurrect German Language 101, with NEIN and JA for yes and no, with no E(nglish). And yes, a ninja is one of a body of trained assassins and spies in feudal Japan (Chambers) and countless Jackie Chan movies. Axis? The best I can come up with is that Japan was one of the Axis powers (Germany and Italy the others) but I’m not convinced their spies were conspicuously ninjas.
18 Backing young man working as part of a network (5)
NODAL young man: LAD and working: ON spliced and reversed
19 Unwell during function — bodyguard’s showing a distinct lack of sense (9)
SILLINESS Unwell: ILL, ((trigonometric) function SINE and (still with the Axis) bodyguard: SS, Hitler’s elite troops
20 Resolve finally to refer upwards in school? (5,2,1,4)
BRING TO A HEAD A double definition
24 Mad king beheaded son (4)
NUTS Our king is CNUT (still better known and typographically safer as Canute) with his head missing and a S(on) attached
25 Large number returned without money as a final blow (2,3,2,3)
TO CAP IT ALL Rather simpler than the impossible version I originally assayed with END instead of CAP: money CAPITAL and large number: LOT “returned” “without” (here outside)
26 Invading Asiatic king is a fine figure of a man (4)
HUNK Your HUN is your invading Asiatic, and K stands for King.
27 Making correct in pronunciation to protect a stack of future memos? (7,3)
WRITING PAD Sounds like RIGHTING, and is protected by a PAD.
1 Give over house to headless haunter (4)
HOST A rather elaborate definition, but it works. Your haunter is GHOST with its head, in time honoured fashion, missing.
2 Time to follow up on service for flying boat (4)
RAFT Service for flying: the RAF, T(ime) following. What you do with the “up” is optional.
3 Cease to care and get rid of personal sprite (3,7,2)
LET ONESELF GO In crossword where such phrases have one’s rather than your, ONE’S ELF would be the personal sprite. LET GO on the outside is a common euphemism for sack, make redundant, etc.
4 Bitterness about golf balls? (5)
BILGE Bitterness: BILE, golf Nato for G to be inserted. I’ll leave you to decide whether the definition is a little too vulgar, this not being Sunday.
5 Hard to listen to peacekeepers on “Oh, What a Lovely War”? (9)
UNMUSICAL Peacemakers: UN, the query on “Oh What a Lovely War” allows definition by example of a MUSICAL
7 One dealing with lots of upset EU reaction (10)
AUCTIONEER Once you recognise where the definition ends, simply upset EUREACTION
8 Unfortunate amnesia about that dressing (10)
MAYONNAISE Create an “unfortunate” version of AMNESIA and smear it tastefully around YON for that.
11 Examine row of birds from northern Europe (12)
SCANDINAVIAN An easy charade. Examine SCAN, row: DIN, of birds: AVIAN
13 Senior politicians take lead for seat (5,5)
FRONT BENCH Take lead: FRONT, seat: BENCH. Pretend not to see the “for”
14 Had composer of Peter Grimes promoting mariner’s end as cynical (4-6)
HARD BITTEN Composer of Peter Grimes is BRITTEN (watch for about 90% of choral societies in the UK performing his War Requiem in November this year). Stick the en claire HAD on the front while promoting the R from the end of mariner. The clue has some correspondence with the plot of the opera
16 Wash out club that has a dirty look (9)
DISCOLOUR Chambers gives “take away colour from” as one meaning, so that will do. Club is DISCO, and dirty look is LOUR.
21 Try tango, love (5)
HEART Tango is Nato for T, attached to try: HEAR.
22 Papa very angry over result of condensation (4)
DAMP and Papa is Nato for P tacked on to MAD for very angry, reversed
23 Stupid person is left trapped by hoax (4)
CLOD L(eft) in COD, which is not just a fish but also a hoax.