The unclued lights (three of two words), individually or paired, are of a kind, with 1 Down as a plural. Two of these unclued lights do double duty to reach the number indicated in the title. Ignore one apostrophe and, elsewhere, an acute accent. Chambers does not confirm 25A.
 

Across

 
1    What a professional soldier might expect to earn? (13, two words)
9    Regularly got across propellers (4)
11    English specify new law about kitchen equipment (10)
12    Knight left country singer (4)
16    Was in French estaminet, confused with the absence of small men (5)
17    A common waif (5)
20    This gives some writers valuable tips (7)
21    Scared to bits, Phoenicians drop tattered hose (7, two words)
23    Keep away from one very dead (7)
24    Inexperienced, but is on course (5)
25    Cornish castle lacking hair lotion and old Spanish wine (5)
30    Have the assembled groups succeeded? (7)
32    O’Neill’s converted 70s Bishop of London (7)
37    Game bird, not one characteristic of the country (5)
39    Treasured, certainly expensive (4)
40    Monster fowl getting at cereal (10)
41    Punch cut game (4)
42    Bestseller let off for fine writing (13, two words)
 

Down

 
2    Big jar, so to speak? (5)
5    Admit you’re the type to leave a mark (7)
6    Shy, eating end of meal in front of Gasthof, over-indulging (7)
7    Form of art, adapted in composition (6)
8    Doctrines people found inside apartments (9)
13   Plant up to now mostly found in Lincoln (7)
15   Charity contradicts accepted pedestrian code (8, two words)
21   On trial for harbouring? (9, three words)
22    Measure the depth again of boom on channel? (7)
29    Fish when one is in position (6)
31    Road providing disturbed rest over centre of Exeter (6)
33    Poet’s not right for watch (5)
34    Fright — lose head and slip (5)
35    Digs out dead little creatures (5)
 
A first prize of £30 for the first correct solution opened on 2 May. 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 2256, The Spectator, 22 Old Queen Street, London SW1H 9HP. Please allow six weeks for prize delivery.