The unclued lights are broadly of a kind (33 differs from the others, though 33K would have been more appropriate, if it fitted in!). Each one Across can somehow be paired with a Down one. Elsewhere, ignore one accent.
 

Across

 
4    Reacting slowly, having felled lime-tree with ease, almost (11, hyphened)
11    Lizards from Asia – gnu involved (7)
12    Indian nationalist heading for reform without English involvement (6)
14    Roman soldier covering a great distance (5)
16    These rain-clouds aren’t on my premises, I say (5)
19    Oarsmen’s strips (7)
21    Small key rented out timelessly (4)
24    And others...