Clue: Epistolary novel: badly written letters in yarns? I opt out (this was pre-GCSE) (1,5)
Answer: O-LEVEL
Explanation: Definition: his was pre-GCSE
***(elovel)**, being the letters of "epistolary novel" with the letters of "yarns i opt" removed [*out*], so "**E**(pisto)**L**(ary n)**OVEL**"