Pretended to eat mushroom and swallowed (8)
I believe the answer is:
accepted
'swallowed' is the definition.
(swallow can mean to accept a story or claim)
'pretended to eat mushroom' is the wordplay.
'pretended' becomes 'acted' (I've seen this before).
'to eat' indicates putting letters inside.
'mushroom' becomes 'cep' (name for Boletus edulis - an edible mushroom).
'acted' going around 'cep' is 'ACCEPTED'.
'and' is the link.
(Other definitions for accepted that I've seen before include "Tolerated; believed to be correct" , "Said 'yes'" , "Received; approved" , "Conventional -- customary" , "such behaviour normal?" .)