Divert first of lorries in error (7)
I believe the answer is:
deflect
'divert' is the definition.
(thesaurus)
'first of lorries in error' is the wordplay.
'first of lorries' becomes 'l' (1st letter of 'lorries').
'in' is an insertion indicator.
'error' becomes 'defect' (I've seen this before).
'l' going inside 'defect' is 'DEFLECT'.
(Other definitions for deflect that I've seen before include "Cause to go off course" , "Change course" , "Turn aside or deviate from course." , "Swerve" , "Turn from straight course" .)