GenUKI Gloucestershire has an 1830 Pigot's Directory of Bristol.
This shows Gibbons & Garrett, Miller, Hook's Mills, Bristol?
And in the Edinburgh Gazette, 26th February 1830:
Daniel Gibbons and Christopher Garrett the younger,
of Hook's Mills, Saint Paul's, Bristol, Gloucester,
millers.
In fact, as far as I can remember, Hook's Mills was just the name of an area of Bristol, rather than a mill as such.
In fact, the CofE Girl's Orphanage was founded there in 1795?