In 27 clues the wordplay leads to the answer with an extra letter which is not entered in the grid. In clue order, these letters spell out thematic material. 4 answers are clued without definition. Solvers should indicate a fifth instance in the completed grid.
ACROSS
1 It's a mount backed before (4)
4 Goes off card games? (4)
7 Raise mood of counsellors (5)
11 I open a drink can (recycled) with such a mechanical device? Hardly!
(13)
13 He's sadly impeded after ignoring politician (5)
14 Fisherman's laugh about learner (8)
15 A head of royalty in millennium year could be so addressed? (4)
18 Struggling voter accepts a source of inspiration (5)
20 That's about rage (3)
21 Furniture material's central part put back and left (4)
24 Animal writer that lady's found a highly amusing person! (7)
25 French actress's tangled amour with Etienne at first... (6)
27 ....she's game to begin with in her bedchamber (6)
29 Pastorals with no introduction could make you perplexed (7, 3 words)
35 Sailor protects ship for old ruler (4)
36 24's city (3)
37 Confused mariner here? (5, 2 words)
39 A lack recalled in old colony (4)
40 West Coast state's drivers' body touring the plant (8)
42 Impossible to capture queen (5)
44 Method of payment thwarted Central European reportedly (13, 2 words)
45 Liberally, theatrically (5)
46 Mineral found in volcanic rock supplies region (4)
47 I leave nest to find Charlotte's girl (4)
DOWN
1 European Union soldiers, male, in charge of deserts (6)
2 Not much time added on (3)
3 With elbow out, carry almost topless girl (dim) (6)
4 Poles are seen by the French coming in making a mark (6)
5 1938 AD? (9)
6 Thorny bowling (4)
7 High point as ruling power's overthrown without a hint of malice (5)
8 Reality TV's essentially flawed (6)
9 One in ten two-time periodically (3)
10 Lose bit of composure in unseemly encounter on the way (7, 2 words)
12 Good guy's found in rye working (11)
16 A run out, look ! openers in Third Test - described by him? (6)
17 Back fighting again? (4)
19 17 could become excellent (4)
22 A new person, top quality, in flying business (9)
23 Pitman's short dog (6)
25 Scotsman embracing everything about walking aid (7)
26 Lease changed otherwise (4)
28 Fat boy devours new recipe (4)
30 Learn regularly in school (6)
31 NZ white exchanges taps in reordered package (6)
32 It's sweet of the French artist - gosh! (6)
33 Theme of narrative - trouble, Newcastle area's absorbed by itself? (6)
34 Girl scapegoat (5)
38 Overhead could show it? Yes and no! (4)
41 Member's right to participate in company gathering (3)
43 On reflection regret love of monarch's (3)
To enter this competition send your entry, including the highlighted fifth instance, in list format to me at derek@crosswordcentre.fsnet.co.uk to arrive before the 8th September. The first correct entry picked will receive a copy of Chambers Concise Crossword Dictionary which has been donated by the publishers.