Fans of classic 12 will know that where ‘Q’ = ‘the number of’: Q26 x Q1D x (Q34 + [Q36D/5A x Q15D]) x Q14/20 = Q the puzzle. 14/20 is four words in total.
 

Across

 
1 Red vestment eastern compère retains (6)
10  Seeds of casaba once processed (10, two words)
11  Ruth from the East posed outside for painter (6)
15  Contralto with yen for bonbons (5)
16  Blissful Enid cycling in the City? (6)
22  Analyst’s father exactly mirrored John (8)
23  Quiet rivers fuel wells (7)
24  Crosses as decorations (4)
25  Criminal idle in old age (4)
27  Take a bath beside fellow washer (7, hyphened)
29  I make good veg with recipe embracing seaweed (8)
32  Very end of awful row (6)
35  Vessel carrying liquid has afternoon inside a Baltic port (5)
36  Rose Walker runs with author Eric (7)
37  Gossip too much about dye (6)
38  Thinner ray swimming in this sea? (10)
39  No king came down late (8)
40  Spaniard nurses raving mad snail (6)
 

Down

 
2  Bill presses followers to reform (5)
3  Broad-bladed knife that’s noble and grand (6)
4  Plant extract trainee Christian denied men (7)
5  Fire-shovel marmelized insects (10)
6  Restless dieters went off and smoked (7)
7  Popular almost incredible drug (5)
8  Barking loud, Oscar gave full worth in exchange (9, two words)
9  Some unsung star (3)
13  Most stupid prune sent up by silly set (7)
17  Fluxes in clownfish (skinned and pickled) (7)
18  Shifty patterer journo dealt with earlier (10)
19  Duke and lord rule by brute force (7, hyphened)
21  Pedigree pet Reagan trained (9)
28  Trachea you and I had a hospital probing (7)
30  Wander round station in alpine resort (6)
31  Prosperous type so long at the big house (5)
33  Reduced receptacle holding outstanding letters within (5)
 
A first prize of £30 for the first correct solution opened on 20 August. 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 2370, The Spectator, 22 Old Queen Street, London SW1H 9HP. Please allow six weeks for prize delivery.