Financial Times 13,323 / Jason

One could say this was a gift of a puzzle because by and large most answers were easily obtainable, though I have minor reservations about 7, 18, 19 and 23dn. The parsing for 14dn took a few minutes to spot but the rest was quite straightforward.

Across
1 BALLET  TELL (inform) A B (bachelor) reversed
4 PROHIBIT  PRO (for) I (one) B[oar] in HIT (punch)
10 SANDPIT  S (succeeded) AND (with) PIT (stone)
11 SARDINE  *(SARNIE D)
12 BOON  BOO (disapprove) N (new)
13 GAINSAYERS  GAIN (increase) [Dorothy L.] SAYERS
15 BESTOW  BEST (first) OW (expression of pain)
16 SUNDOWN  UNDO (let loose) in SW (south west) [battalio]N
20 BELLBOY  BELL (ring) BOY (lad)
21 BOUNTY  triple def.
24 LABORATORY  LAB (the left) ORATORY (art of public speaking)
26 BENT  BE (live) NT (National Theatre)
28 SUNRISE  *(NURSE IS)
29 DESPAIR  *(PRIDE AS)
30 ABSINTHE  ABS (sailors) IN THE
31 FEDORA  FED (FBI man) OR A (American)

Down
1 BUSHBABY  *(BU[t] SHABBY)
2 LANGOUSTE  *(SLOANE GUT)
3 EXPO  EX (former) PO (pilot officer)
5 RESINOUS  RES (residence) IN O (old) US (America)
6 HERE AND NOW  HER (that girl) *(DONNA WE)
7 BRIBE  B (black) in BRIE (cheese) – ‘spot’ does not form part of the wordplay and is superfluous
8 TEENSY  dd
9 STRAW  WARTS (growths) reversed
14 DOLLAR SIGN  DOLLAR (5s) SIGN (token) – dollar is an old slang term for five shillings (5s)
17 WINNEBAGO  I (current) in *(WE BANG ON)
18 DOG-TEETH  dd – though the second one should really give dogtooth violets rather than dog-teeth
19 HYSTERIA  *(IS EARTHY) – ‘group’ as an anagram indicator?
22 PLASMA  PL (Poet Laureate) AS (like) MA (Mum)
23 PRUDE  P (pressure) RUDE (cheeky) – a schoolmarm is a prim, pedantic woman rather than a prude
25 BONUS  B (born) ONUS (responsibility)
27 ISLE  I (one) [has]SLE