The boy is at Bognor, say (5)
I believe the answer is:
regis
'bognor say' is the definition.
I know nothing about this answer so I can't judge whether this works.
'the boy is' is the wordplay.
'the boy' becomes 'reg' ().
'reg'+'is'='REGIS'
'at' acts as a link.
Can you help me to learn more?
(Other definitions for regis that I've seen before include "See 9" , "See 19" , "See 1" , "Bognor or Lyme" , "King's" .)