Criticise daughter engaging in intercourse in tight fabric (7)
I believe the answer is:
spandex
'tight fabric' is the definition.
'criticise daughter engaging in intercourse in' is the wordplay.
'criticise' becomes 'pan' (informal term meaning to criticise heavily).
'daughter' becomes 'd'.
'engaging in intercourse' becomes 'sex' (I can't explain this - if you can you should believe this answer much more).
'in' is an insertion indicator.
'pan'+'d'='pand'
'pand' going within 'sex' is 'SPANDEX'.
(Other definitions for spandex that I've seen before include "Elastic synthetic fabric - expands (anag)" , "material" , "Elastic fibre" .)