Sandown doesn’t have its own beach? (4)
I believe the answer is:
sand
'beach?' is the definition.
'sandown doesn't have its own' is the wordplay.
'doesn't have its' indicates named letters should be taken away.
'sandown' with 'own' removed is 'SAND'.
(Other definitions for sand that I've seen before include "Granular substance" , "Yellow-brown colour" , "Granulated quartz" , "Polish" , "Egg timer grains" .)