Seasons Greetings 7 by Eclogue

The grid is in the form of a Christmas cracker.  In 30 clues, the wordplay leads to an extra letter, not required by the definition - in clue order these letters provide a clue to the theme, which is omitted from the wordplay (which provides the entry) of the remaining 10 clues, while the definition refers to the full answer.  Solvers should highlight the thematic character hidden in a straight line in the completed grid. Numbers in parentheses refer to grid entries. Chambers (2014) is recommended, including one abbreviation, but not the common compound at 2d

1 Wild asses trail round fertile spots (5)
6 Bard’s restrained by his own power, returning kiss tribute to dead (8)
14 Large cells active silicon lined with copper (4)
17 Student’s very quiet in the pub (4)
20 My grasping the way early English’s leading appreciation of feeling (7)
22 It’s dirtier forbidding one to miss the mark (7)
23 Capital protection power alongside ear, nose and throat (5)
25 Primarily masked all arrogant persons’ snooty faces (4)
26 O’Brien for one, put down Perth’s plant (10)
27 Stud crests excitedly - explodes (10)
29 Manservant’s farewell (4)
31 Arctic person’s oddball son cast off knitting union suit (5)
32 Guaranteed to be accustomed to protecting senior (7)
33 Is artist always backtracking in old card game? (7)
34 Consumer of alcohol, perhaps, left every tavern nicely addled at first (4)
35 Norman pops in juniper berry (4)
36 Rehash her reasty rubbish (8)
37 Salient local father kept in check (5)
2 The cost of flying airman recruit around Northern Ireland remote base (7)
3 French girl is taken by sister’s fountain pen (7)
4 She’s a brilliant mother (4)
5 Portfolio has stand in inverted wines (7)
6 Private interest’s condition arises in violent sport (7)
7 More ostentatious jaunty hero wins (7)
8 However much butts will hold, but for standards (not European) (7)
9 Colourful swimmer ma’s cooked in meal (7)
10 Habituated by sporting suede on half of digits (6, two words)
11 Recorder to rip into Frenchman’s volte-face (7)
12 I’d sentry punished for thickness (7)
13 Will's denier of own true feelings may take action against drug addict (7)
14 Bazooka’s projectile, perhaps originally aimed toward lumbering machine (3)
15 Loathing turned inward is hardest to reform (7)
16 On clay espy fruit of the daisy family (7)
17 Senior Royal Society since forgotten (4)
18 French city shifted northern borders (5)
19 Headband removed from Scotsman Ian (6)
21 Unruly bint with answer to Mayo’s top of the morning (5)
24 Water buffalo managed within borders of America (4)
28 Clever section in Church (4)
30 Festival’s prelude includes verse in addition to Burns (3)
To enter this competition, send your entry as an image or in list format indicating the highlighted thematic character,  to before the 8th January 2016.The first correct entry drawn from the hat will receive a book from the Chambers range which has been donated by Chambers.