All the unclued Across lights are of a kind, as are all the unclued Down ones. They can be paired appropriately, and can be confirmed in Brewer.
 

Across

4    What’s blocking criminal courts I bet around five? (11)
11    Land adviser returning to wharf without question (7)
16   Suave young socialite leaves broadcasting (5, two words)
21    Not half remarkably rapid. It’s the limit! (4)
23    Surrounded by endless birdsong, aim and shoot (7)
24    Concert walk at the seaside (4)
25    One going in lower, not both (7)
30    Select group making lake bed, first (7)
31    Bird to drop head for nothing (4)
34    Wild ox hiding in the midst of shanty aboard (4)
35    After snarl-up, motorists’ group’s taken over in charge of island (7)
37    How the heats are contested? (5)
40    Society member working by farm in the south of France (5)
41    Restrict beer supplies in principle (9)
42    Assassin’s butt by the river (6)
43    Words of warning for the present and times gone by (7, two words)
44    Intercept bad ball, ignoring wings, moving to middle (11)
 

Down

1    One can sit through this crux if one tries (11, two words)
2    Building expert missing from introduction by sailor (6)
3    Thought of employment in Maryland? (5)
5    Number three in aquarium feeding young male dolphin (4)
6    Spoke of heartless descendant of Fatima (4)
7    Ditch in the south-west — attempt return from orbit here? (7, hyphened)
8    Spoke of 3-D changing room (7)
9    List of places I attempt to go round in time (9)
10    He calls at five. Is it — or later? (7)
15    Pool equipment, extremely tacky (5)
18    Excitability of one from a Nielsen symphony? (11)
20    Nothing’s wrong, honest — it’s just a unique attempt (7, two words)
27    Banal letter with dog (7)
28    Courtier clergyman in incorrect speech? (7)
29    What brightens gloom? Outrageous clothing dandy adopts (7, two words)
33    Go on together for cake (6)
38    Some conservatoire backing debauchery (4)
 
A first prize of £30 for the first correct solution opened on 29 October. There are two runners-up prizes of £20. (UK solvers can choose to receive the latest edition of the Chambers dictionary instead of cash — ring the word ‘dictionary’.) Entries to: Crossword 2380, The Spectator, 22 Old Queen Street, London SW1H 9HP. Please allow six weeks for prize delivery.