The unclued lights (individually or one pair) are of a kind. But, before entry into the grid, all but one has to be adapted figuratively speaking, so that one or two characters appear in an unchecked square.
 

Across

 
4    Most Britons could become members of a band (11)

11    I’ll join regiment under canvas, on the move (7)

13    Was boisterous – I’ll return, danced around (9)

14    Animal, one with fur on (5)

16    Dirty article removed for relation (5)

19    Aim is to keep safe, that’s for certain (7)

21    In torpid lethargy (4)

23    Danced the night away in hell with secondary pupil (7)

24    Oddly, team...