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Thank you to Moo (some nice surfaces here). Definitions are underlined in the clues.
Across
1. Quarrel with Hell’s Angel snorting coke (6)
BICKER : BIKER(descriptive of a member of the Hells Angels Motorcycle Club who rides a motorbike) containing(snorting) C(abbrev. for “coke”, informal term for cocaine).
4. Demote judge jailing English member (8)
RELEGATE : RATE(to judge/to assess) containing(jailing) [ E(abbrev. for “English”) + LEG(member/part of the body, in this case, one of the limbs) ].
10. About to join guru in boat (7)
CORACLE : C(abbrev. for “circa”/about or approximately, when refering to dates) plus(to join) ORACLE(person regarded as the authority of something/a guru).

11. Adjust temperature and go (7)
TWIDDLE : T(abbrev. for “temperature”, in physics) plus(and) WIDDLE(to urinate/”go” in slang).
Defn: … by turning or rotating, say, a control knob.
12. Time spent in a stupor, one might say (4)
DAYS : Homophone of(…, one might say) “daze”( a state of being confused/almost unconscious/stupor).
13. Damaging copies I run off (10)
PERNICIOUS : Anagram of(… off) COPIES I RUN.
16. Get the better of old fool obstructing you (6)
OUTWIT : [ O(abbrev. for “old:”) + TWIT(a fool/idiot) ] containing(obstructing) U(“you” when texting).
17. Interview extremely disagreeable lawyer (7)
DEBRIEF : 1st and last letters of(extremely) “disagreeable” + BRIEF(a lawyer/a barrister who argues a case in court).
Answer: To interview/question someone about a completed mission.
20. Happy about copper, one close to the Sun? (7)
MERCURY : MERRY(happy/joyful) containing(about) CU(symbol for the chemical element copper).
Defn: A planet, ….
21. Dictator’s truthful sound (6)
STRAIT : Homophone of(Dictator’s) “straight”(truthful/honest).
Answer: A narrow stretch of water connecting two wider areas of water.
24. Old lady thriving in Scottish town (10)
MOTHERWELL : MOTHER(for whom an informal term is “old lady”) + WELL(doing comfortably/thriving).
25. Thought assistant’s article misplaced (4)
IDEA : AIDE(assistant/advisor) with “a”(an article in grammar) moved to the end(misplaced).
27. Put down American writer (7)
ASCRIBE : A(abbrev. for “American”) + SRIBE(a writer/journalist).
Defn: …/to consider someone or something to have a particular cause, as in “The crash was put down to engine failure”.
29. Delivery that kangaroo might be proud of? (4,3)
LONG HOP : A sufficiently long leap that would make a kangaroo proud.
Defn: In cricket, a delivery by a bowler that bounces relatively near the bowler.
30. Conservatives leaving city centre in a mess for years (8)
ETERNITY : “C,C”(2 x abbrev. for a member of the Conservative Party) deleted from(leaving) anagram of(… in a mess) “city centre”.
Defn: …, if not forever.
31. Sacked John and another Kennedy (6)
LOOTED : LOO(in North American slang, a toilet) plus(and) TED(another Kennedy, in this case, a brother of John F.)
Down
1. Sneaky way of getting into house? (8)
BACKDOOR : Double defn: 1st: …/describing a way of achieving something by dishonest or indirect means.
2. Way in which you might end up bankrupt (5,6)
CAREY STREET : The street/way in Central London where the bankruptcy court (in which you might be declared a bankrupt) was situated.
3. Every bishop retiring from water’s edge (4)
EACH : “b”(abbrev. for “bishop” in chess notation) deleted from(retiring from) “beach”(sandy shore at the water’s edge)
5. Hard put to it, as family may be (8)
EXTENDED : Double defn: 1st: …/having to exert utmost effort to do something/it); and 2nd: …, one that includes grandparents and other relatives.
6. English creative’s misshapen gut (10)
EVISCERATE : Anagram of(… misshapen) [ E(abbrev. for “English”) + CREATIVE’S].
Defn: To …/to remove intestines and other internal organs/viscera.
7. Unfinished opera getting financial assistance (3)
AID : Last letter deleted from(Unfinished) “Aida”(an opera by Verdi).
8. Still odds on, with last withdrawn (4,2)
EVEN SO : EVENS(in betting, the chances/odds of winning equalling that of losing, either losing or winning the amount bet) + “on” minus its last letter(with last withdrawn)
9. Virile chaps exposing themselves in Bethlehem? Enough! (2-3)
HE-MEN : Hidden in(exposing themselves in) “Bethlehem? Enough”.
14. Obvious opposites (4-3-4)
OPEN-AND-SHUT : Combination of two antonyms/opposites.
Defn: …/indisputable, with reference to an argument or case.
15. Caution? Consider it absurd (10)
DISCRETION : Anagram of(… absurd) CONSIDER IT.
18. Bully done in after start of boozy argument (8)
BROWBEAT : BEAT(done in/exhausted, as in “I’m beat after all that”) placed below(after, in a down clue) [ 1st letter of(start of) “boozy” + ROW(a noisy quarrel/argument) ].
19. Last of thieves caught and flogged (8)
STRAPPED : Last letter of(Last of) “thieves” + TRAPPED(caught/shut in).
Defn: …/beaten with a strip of leather.
22. Spike mischief-maker’s beer? (6)
IMPALE : IMP(a mischief-maker/troublemaker) + ALE(a style of beer).
Defn: To …/pierce with a sharp point.
23. Some endlessly lying in underhand way (5)
SLYLY : Hidden in(Some) “endlessly lying”.
26. One in Spain concealing daughter’s ruin (4)
UNDO : UNO(the number one in Spanish) containing(concealing) D(abbrev. for “daughter”).
28. Occasionally crude hint (3)
CUE : 1st, 3rd and 5th letters of(Occasionally) “crude”.
Nho the bankruptcy court’s address and stared at the crossers looking for a phrase like the opposite of Easy Street. Other than that a gentle stroll, ta Moo and scchua.
Got off to a very good start on this then slowed down
Enjoyed it. Favourites included: MOTHERWELL, RELEGATE, CORACLE, LOOTED
Never heard of Carey Street
Thanks Moo and scchua
I only got Carey Street thanks to wordfun.ca . . . I initially had Queer Street but that rendered other answers impossible and/or redundant. Other than that, a satisfying solve. Thanks to Moo etc.
Was Moo in a dark frame of mind when setting this? There were lots of references to financial ruin, venality and bullying in this grid.
I liked the generally succinct cluing in, for instance, OPEN-AND-SHUT, and Moo’s particular brand of humour in HE-MEN. LOOTED was also very neat. CAREY STREET was a guessing game and like Eric E, Queer Street occurred to me though by then, I had all the crossers that nixed that idea.
Very enjoyable.
Thanks Moo and Scchua.
Thanks Moo and Scchua
2dn: I think a one part clue for CAREY STREET would be unfair in most other newspapers – but let us not forget that this crossword is in the Financial Times.
Yes good fun and straightforward except I’d never heard of Carey street either.
Some good anagrams, esp pernicious, eviscerate, and discretion. Liked looted vm.
I tried solving shorter clues first (mrpenny’s solving method) which I really liked
I agree with Diane’s praise of the succinct clues and humour. I ticked SLYLY, LOOTED, EVISCERATE, STRAIT, IMPALE, DISCRETION.
I also had to reveal CAREY in 2. Unfortunately the clue gave no hope of getting the answer – you either knew it or you did not.
Thanks Moo and scchua
I can’t remember where I heard it and I didn’t know about the location of the court, but I finally managed to drag Carey Street out of my rapidly decaying grey matter to make it my LOI.
I wonder what else is in there…
Otherwise good clues, fun to complete and a nice blog. Thanks both.
Loved the clue for ETERNITY.
Queer Street, that was the lurking expression, thanks Eric @3. Struggle Street is another, similar.
Some lovely clues as always form this setter. I’ve never heard of Carey Street, and would never have guessed there was a specific court for bankruptcy hearings. Thanks to Moo and sschua