'THANKS TO ____________________________' by Apex

Apart from 4 down, clues are presented in symmetrical pairs and the clues in each pair are separated by one redundant word. In numerical order of clues the initial letters (4 words) of redundant words complete the title of the puzzle. The unclued perimeter (clockwise from square 18) and followed by the central row (8 words) precede the title of the puzzle. Unchecked letters in perimeter and central row could give - 'EXAM CLUE - A CLOWN'. Chambers Dictionary (1998) is recommended but does not give 15 down (in Collins).

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Across
8,34 Following on time to worry many - little time to secure match (4,4)
9,33 Bad act, I shall go outside to watch man about to perform (7,7)
10,32 Letter about grievous old rogue of Troy I claw back (5,5)
11,31 Some tasting wine supporting new Scottish venture (4,4)
12,30 Idiot - not the first airman encouraging old to go short of course! (3,3)
13,27 Italian children desire mother to meet orchestra (4,4)
14,25 Fellows in mine love fruit, another medical officer tense in gala opening (7,7)
18,24 Lear's crazy to pinch hard stone, newest attraction to steal with difficulty (6,6)
20,22 Weight to strengthen man going around, latest plant a success in pool (5,5)
Down
1,26 Queen in raid upset, king expecting a new tie destroyed ribbon (5,5)
2,30 Stink about knight embracing English youth, women in benefit about to cry (4,4)
3,29 Old giant, to get European climbing apple tree, to curb nothing (4,4)
4 Kind of force to adopt before turning up object (13)
5,25 Uprising on every plain - now underground in some trouble (5,5)
6,23 Scots allowing nutlet to burst, does inferior god fear about opening of shell? (6,6)
7,28 Primitive in charge of amber liquid denounces a mob demolishing lectern (4,4)
9,21 A smoother Irish expert encounters bird following fellow in university (6,6)
15,16 A hero, US railroad detectives always hammer a bird that steals (5,2 words,5)
17,19 Complain no more, soldiers with little energy now ignore rebuke (4,4)