Well-phrased wordplay and clues on the whole. I struggled with several, to my mind, esoteric refs (SQUEERS, OSBERT, TREVELYAN) but I’m sure someone better educated (in Britain!) than myself would not have been challenged.

Across

Down

I found this a very tough puzzle, esp the lower half but also the long 20-letter phrase in the top half which was new to me.    But I got there in the end and there were some excellent clues.   Solving time, 61 mins.

* = anagram   < = reversed

ACROSS

1 DOG LATIN   (an old git)*    There’s nothing more to indicate the anagram than ‘from’ as far as I can see, which is unusual.

5 A DON IS (lives)     From Greek mythology

12 GA (SO H) OL    can = gaol

18/10 THREE SHEETS TO THE WIND     New to me, it means very drunk.   (he who detests thirteen)*     I noticed from the start that ‘thirteen’ was spelt out rather than shown as 13 which is usual practice when referring to another clue.   So I was not sure if it referred to 13 ac (BEVERAGE) or the number.    In the end it referred to the answer of course and the ‘thirteen’ was used as it was part of the anagram.    I was very slow getting it because (1) I’d one mistake in a crossing word at first (2) did not spot the anagram and (3) had never heard the phrase, which I verified after.

23 A RIA DNE   a (end air)<   More Greek mythology.

25 C (ONCE R) T   R = king   ct = court   once = when

26 MAJORITY VERDICT   A tip-top cryptic definition that I tumbled to only when I’d quite a few crossing letters.

27 NA (N) TES    nates is a technical work for the buttocks (can’t say I’ve ever heard used, but it’s in Collins).

28 CROSS MAN   “Diaries of Mister X!”       This was the last I got, and I did wonder if the younger generation might struggle with the reference.   It’s to Richard (Dick) Crossman, Minister in the Labour Government of 1964-70 who later wrote extensive diaries about the experience.    I know Eimi’s said the Indy’s not always strictly Ximenean - it’s a stretch to define Crossman as ‘diaries’, I’d say.

DOWN

1 DES RES    Desires less I

2 GREAT BEAR    bear = stock market when share prices are falling.

4 INTER    Inter Milan (football club) play at San Siro.    Inter = Bury and Bury is a Football League team that  readers may be surprised to know never appeared below the top two divisions from their election to the League in 1894  till 1957.

14 A (are - metric measure) N C( l)IENTS    l = money (£)

16 CARPE DIEM   (from Latin - enjoy the present - literally seize the day) (made price)*

17 Ralph S (TE) AD MAN   TE Lawrence, writer.

19 ENDOR S(af)E   Definition = second.    The rest from Star Wars.

21 CONTRAS    Amusing reference to Oliver North so nothing to do with the point of the compass.

22 STAT IN    Stat = photostat

24 INJUN   “Honest Injun” contrasted with those using ‘forked tongue’ i.e. lying.

25 C (see) OVER   A fielder (cricket)

A little harder than usual from Quixote, I found. Solving time, 31 mins.

Notes on some clues below - happy to explain others if asked.

ACROSS

6 S (last letter of chips) CUP Was looking for ‘cha’ for a while.

14 IRREGULAR VERBS As ‘do’ and ‘have’ are - good.

25 GO B A (NANA) S Gob = spit, as = when, nana = granny

DOWN

5 RASPBERRY Double definition

7 COULOMB “Charge physicist” The unit of charge, named after the physicist - a little surprised that the two parts of the clue were not more distinct.    Or, maybe, a cryptic definition is intended, though then I thought there would have been a “?”

20 PAST Y i.e. at the end of the dictionary (under Z)

21 D (WEE) B Db = decibel (bit of noise)

A fairly routine puzzle from Mudd here. I completed it fairly quickly because I found the clues for the three long answers easy. Still, 11A and 5D took some puzzling over.

Across
9. REAPPORTIONMENT - anagram of IMPORTANT ONE PER
10. SAUDI - S (small) + AUDI (car)
11. HAMSTRING - HAM (amateur) + STRING (racehorses)
12. AMERICANS - RIC[h] (infinitely wealthy) in A (a) + MEANS (way). Do I have this right? I must say that I do not exactly see how “infinitely wealthy” can properly clue RIC.
14. HEART - HEAR (try) + T (temperature)
16. SADOMASOCHISTIC - anagram of STOMACH ACIDOSIS
19. REACT - R[ubbishing] + E[xams] + A[nd] + C[ritiques] + T[eaching]
21. LITTLE TOE - LITT[er] (2/3 of piglets) + LET (allowed) + O[n]E
23. CARPENTER - PEN (pound) in [Jimmy] CARTER. A “chips” is a carpenter, I guess.
25. SWEAT - anagram of WASTE
26. PUBLIC OWNERSHIP - PUB (local) + COW (Jersey) in LINERS (vessels) + HIP (with it)

Down
1. TRESPASSER - TRES PASSE (very dated in French) + R (king). Nice clue!
2. MANURE - MAN (isle) + URE (river)
3. OPTIMISM - OPT (PICK) + S (Sweden) in MIMI (girl) backwards
4. ARCH - [l]ARCH. Oh, “arch” again. We had that last week!
5. SIAMESE CAT - I AM (I am) + E[xtend] + S[econd] + E (note) in SCAT (jazz)
6. SNATCH - double definition
7. HESITANT - HE (man) + SIT (pose) + ANT (six-footer)
8. STAG - S (short) + TAG (leg)
13. ABSOLUTION - even-numbered letters in MAYBE THE ANSWER RELEASE
15. TICKER TAPE - double/cryptic definition
17. DIATRIBE - DIA (help raised) + TRIBE (people)
18. ILLUSORY - anagram of OUR SILLY
20. TIEPIN - TIE (game) + PIN (leg)
22. TEETHE - TEE[nagers] + THE[ory]
23. CAPE - double definition
24. RANK - double definition

Blimey, that was tough! It didn’t help that I’m nursing a hangover from last night (beer tasting event) but I think I’d have struggled anyway. Took about 45 minutes, but I had to use reference books to finish it.

Across
1 TRIP,OD=do rev.
5 AP(PRO)ACH(e) - I totally misread this at first, looking for AC(e) inside a type of native American, meaning detail.
9 PARSI,FAL - an opera by Wagner. I had to look up Parsi, as I thought it was just a language. The Fal is a river in Cornwall.
10 RESCUE - R.E.’s cue.
11 CHAMPIONSHIP - as the English football 2nd division is now called.
13 ANNA - an obsolete Indian coin.
14 N(I,COT)INE - I had to check this in the dictionary - a cot is a small cottage.
17 STA(R,FI)SH
18 PARE - sounds like “pair”, and an anagram of 2d.
20 NUCLEAR WASTE - hidden, but at first I tried to make it an anagram of “menu clear was”.
23 ETH(the*),I,OP - the capital of Ethiopia is Addis Ababa, but maybe it gets shortened to Addis. Would be odd though, as the name literally means “new flower”.
24 INFERNAL - i.e. FERN inside nail*
25 F(RAGMEN)T - which might get him into trouble with colleagues at the Guardian!

Down
2 REAP - confirmed as it has to be an anagram of 18ac, but I don’t get the wordplay. As it’s Araucaria, my best guess would be A in REP, with REP meaning sure, but the dictionary doesn’t back that up. [ As has been pointed out, it's hidden in "InsuRE A Possible" - d'oh! ]
4 DEFRA,Y - DEFRA is the Department for Environment, Food and Rural Affairs.
5 A SLAP ON THE WRIST (whips as tolerant)* - not sure about “hardly” as an anagram indicator, but it makes for a good &lit.
6 PERFORCE - PERFORATE, with AT removed, around C (number).
8 C(AU,TIONA)RY - TIONA being (into a)*
12 INS,TRUC=curt rev,TOR
19 US,EFUL=fuel* - with source as the anagram indicator? Pfui.
22 WA(I)N