The generalist by Didymus
Apart from 56A, the Across clues, and also 21 Down and 29 Down, are abbreviations, most of which can be easily verified in Chambers Dictionary.
ACROSS
11 Z (6)
12 h (7)
13 Y(6)
14 X (10,2)
15 W (8)
16 V (8)
18 U (5)
19 T (5)
22 S (7)
23 R (5)
25 Q (5)
30 P (5)
32 O (5)
33 N (8)
35 M (8)
37 l (6)
38 k (5)
41 J (5)
42 I (5)
43 H (7)
48 G (5)
50 F (5)
52 e (8)
55 d (8)
56 French writer of unrhymed