Clue: Cause confusion with current name given to Casterbridge, it's said, by intros to Thomas Hardy e-books? (5,1,7,2,3,5)
Answer: THROW A SPANNER IN THE WORKS
Explanation: Definition: Cause confusion
I=symbol for "Current", plus N[ame], after THROW A SPANNER='cast a bridge'="Casterbridge, it's said", plus T[homas] H[ardy], plus E, plus WORKS="books"