Solid figure of Conservative regularly taking Ecstasy (4)
I believe the answer is:
cone
'solid figure' is the definition.
(I've seen this before)
'conservative regularly taking ecstasy' is the wordplay.
'conservative' becomes 'c' (abbreviation commonly used in UK politics).
'regularly taking' becomes 'on' (as in 'on drugs').
'ecstasy' becomes 'e' (informal term for the drug).
'c'+'on'+'e'='CONE'
'of' acts as a link.
(Other definitions for cone that I've seen before include "Tapering solid" , "Shape, the base is a circle and the sides taper up to a point" , "Volcano peak" , "often full of ice" , "Movable plastic bollard" .)