Old group allowing in church cat (6)
I believe the answer is:
ocelot
'cat' is the definition.
(ocelot is a kind of cat)
'old group allowing in church' is the wordplay.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'group' becomes 'lot'.
'allowing in' is an insertion indicator.
'church' becomes 'ce' (abbreviation for Church of England).
'o'+'lot'='olot'
'olot' going around 'ce' is 'OCELOT'.
(Other definitions for ocelot that I've seen before include "South and Central American wildcat" , "Feline of South and Central America" , "Wild cat of the Americas" , "Wildcat -- loo etc (anag)" , "Feline mammal" .)