Developers have offered to spend more than £10 million to transform the derelict Blue Circle cement works.
Callstone wants to build a business park, hotel and restaurant on the site at Upper Beeding, near Steyning.
The proposal also includes 84 houses and landscaping.
Richard Stapleton, an advisor for Callstone, told a public inquiry yesterday the site needed substantial work before any building could start.
He told the inquiry at Horsham District Council's offices, housing must be allowed as part of the scheme or the developers would lose £1.5 million.
Horsham and Adur district councils are opposed to the housing.
The inquiry is expected to end on Friday.
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