The eight minimally clued lights are of a type. The heading, (5,2,5) or (5,5) as preferred, may assist, and should be explained by entrants. The solution will be available here on 22 April. 

ACROSS
1 I (6-5)
7 Scot returns flower (3)
9 Incompetent bigwig (7)
10 Jug of brown and dark mixture (7)
11 Gathers for prayers (8)
12 Disgust father returning cloth (6)
14 Country’s alpen landscape … (5)
16 … a flower design (inelegant) (9)
17 Official record-keeper may err with gratis forms (9)
19 Happen again in more current scenario (5)
21 Groups of soldiers – four perhaps on ship (6)
22 Chris and Fay cooked lobster perhaps (8)
25 Last word about island’s mental deficiency (7)
26 D (4-3)
28 Flower running in either direction (3)
29 S (4,2,5)

DOWN
1 Flower (centre of pansy) arranged (3)
2 Swinger moved by Tom’s entrance (3-4)
3 Ungrateful 9, a knave with the French (5)
4 E (10)
5 Reportedly understands jazz musician (4)
6 T (3-6)
7 Bread and tea on the terrace? Nothing lost (7)
8 R (6,5)
11 A (6-5)
13 Device for waking Rod, suffering with malaria (5-5)
15 H (4-5)
18 Gentleman actor, perhaps, accepts opening Spanish cheese (7)
20 Fancy sound followed by artist (7)
23 Poet as yet obscure (5)
24 Island language (4)
27 26 perhaps, a flower (3)