Six unclued lights are examples of ‘3/4/18’ (four words in total, ignore an apostrophe), a quotation (in ODQ) whose author’s surname (7) will appear diagonally in the grid and must be shaded. Elsewhere, ignore an accent.
 

Across

 
11    Tony and Charlie amid ducks beside Yellow River (7)
12    Men declaimed European decree (6)
13    Ignorant leader nun converted (9)
14    Put back small branch on tree (5)
19    Unlocking device averting an awkward situation (7)
23    Hollow tree’s healthy we hear (7, hyphened)
24    Mailing of eighteenth letter sealed by First Minister (4)
30    Maybe cavalryman chopped up Bursera (7)
31    Mother Hubbard’s instrument (4)
32    Units built by American father and sons (7)
34    Auditor’s course with eggs (4)
37    Mother in frock grand for Sabbath (5)
40    Climber collects stuff about Austria (5)
41    Grandma gutted garfish, small fish and big fish (9)
42    Global pharmaceutist a vivacity imbues (6)
43    Commander brisk and provoking (7)
 

Down

 
2    Miserable Mo missing a supply of tea? (6)
5    Anyone out of the Apple is crazy about Dawn (4)
6    Some land in port (4)
7    Thief’s beginning to discuss crime (7)
8    Wife firmly established acted like a pig previously (7)
9    Nastier ad garbled alternative times for events (9)
10    Old fogey has very alcoholic punch first (7)
15    Hoard money (time for a little miserliness) (5)
17    Balkan republic lacking a high-end jeweller (7)
20    Old lady visits that place for hot baths (7)
22    Where are submarines as a rule? (9, three words)
26    Skipping about, TV butler gives offence (5)
27    Poor worker, nursing condition, is against euthanasia (7, hyphened)
28    Scoundrel submerges warm and dry worm (7, hyphened)
29    Botanical term a plucky petty officer grasped (7)
33    Maroon thread (6)
36    Leghorn perhaps soars like weaver birds (5)
38    Girl’s progress cycling (4)
39    Ox in yard penned by local lass (4)
 
A first prize of £30 for the first correct solution opened on 6 June. 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 2261, The Spectator, 22 Old Queen Street, London SW1H 9HP. Please allow six weeks for prize delivery.