Growth and Infrastructure Bill

I wonder whether my noble friend could help me. It may be that I am extremely stupid about this, but I do not understand why it is not possible for the local authority, as part of its renegotiation, to insist upon these things in any case. Why can it not say, “As part of the agreement we want to do this, but the deal is you do actually get started in the way that we between us decide is a start.” Is there anything illegal in doing that?