Harry fed toddies in Reading Festival? (10)
I believe the answer is:
eisteddfod
'reading festival?' is the definition.
'eisteddfod' can be an answer for 'festival?' (eisteddfod is a kind of festival). I'm not certain of the 'reading' bit.
'harry fed toddies' is the wordplay.
'harry' indicates anagramming the letters (harry can mean to attack or spoil).
'fed'+'toddies'='fedtoddies'
'fedtoddies' anagrammed gives 'EISTEDDFOD'.
'in' is the link.
Can you help me to learn more?
(Other definitions for eisteddfod that I've seen before include "Welsh arts festival" , "Welsh cultural festival" , "arts competition" , "Welsh festival of music and poetry" , "Welsh art festival" .)