Room to manoeuvre in plan to control leak - on the contrary (6)
I believe the answer is:
leeway
'room to manoeuvre' is the definition.
(I've seen this before)
'plan to control leak on the contrary' is the wordplay.
'plan' becomes 'lay' (as in laying plans).
'to control' is an insertion indicator.
'leak' becomes 'wee' (as in taking a leak).
'on the contrary' shows that the letters should be reversed in order (letters in the opposite or contrary direction).
'wee' written backwards gives 'eew'.
'lay' placed around 'eew' is 'LEEWAY'.
'in' acts as a link.
(Other definitions for leeway that I've seen before include "Allowance" , "Elbow room?" , "Allowable margin, latitude" , "Margin of safety" , "Space for free movement" .)