Danscowpie this is drifting way from the ATC related nature of my original post, and its clear you have an axe to grind from your other post.
The Airport land is owned by Southend Borough Council, it can only be run as an Airport under the terms of the lease. Change of use would not be an easy option.
The location itself doe's not suit a haulage depot, and the line would not support freight operations without building a siding of some sort.