Selby Planning Portal
Public Access Portal planning reference 2017/0736/REMM - if you put that in the box and press Search, it will bring up all the supporting documenation.
Urban designer
Specialist Heritage and Urban Design Review for Planning Application - this makes for compelling reading.
National Policy Planning Framework
This is a government document, available from this link that sets out the government's planning policies and how these are expected to be applied.
National Design Guide
Another government document, that illustrates how well-designed places that are beautiful, enduring and successful can be achieved in practice.