Drag queen quits Blackpool attraction (3)
I believe the answer is:
Here is my best explanation:
'drag' is the definition.
(towing is a kind of dragging)
'queen quits blackpool attraction' is the subsidiary indication.
'queen' becomes 'er' (abbreviation for Elizabeth Regina).
'quits' is a deletion indicator.
'blackpool attraction' becomes 'tower' (Blackpool Tower).
'tower' with 'er' taken out is 'tow'.
(Other definitions for tow that I've seen before include "Drag along behind, say barge", "Pull (with rope)", "Prepared fibres", "Pull along (a vehicle)", "Haul", "form of flax", "Pull using cable", "Pull along behind, say barge", "Pull or drag along behind" and "Draw".)