The unclued lights are of a specific kind.
 

Across

 
11    Top flier backs help for sloth (6)
12    Birds on the barriers (5)
14    Mayfly larva on cobras, dead (5)
15    The head that’s characteristic of the Russian Church (5)
17    Lay claim to 32s somehow (6)
19    Eric needs new place to stay (9)
21    Caught fish, mushy peas and wine? (7)
24    Short Celt, retired keeper, in a 2-2 match? (9, two words)
26    Prince, lively, talking idly (9)
30    Spanish muleteer, backward, out east, love (7)
31    Churchmen waving signal around prison (9)
33    Karnataka, formerly, note, has...