Rising prices discovered by Ian in loft conversion (9)
I believe the answer is:
inflation
'rising prices' is the definition.
(synonyms)
'ian in loft conversion' is the wordplay.
'conversion' indicates an anagram.
'ian'+'in'+'loft'='ianinloft'
'ianinloft' is an anagram of 'INFLATION'.
'discovered by' acts as a link.
(Other definitions for inflation that I've seen before include "Increasing costs" , "Drop in money value" , "Economic problem" , "Building costs" , "getting increasingly aired?" .)