The whole General Permitted Development Order - read it and learn it to save money and time when appraising your development opportunities
The Use Classes Order - see whether the building is a shop or professional services or a bank or a warehouse or...
With Special Thanks to Steve Speed a clever diagram showing how to use Permitted Development.
Your starting point for all things regarding Planning Permission
A massive resource that every developer should have in their knowledge base
Is your building listed?
Find your Local Authority, Parish and County councils
Land Registry- login and find out who owns the property you're after
The National Planning Policy Framework - the backbone of planning policy
The Planning Practice Guidance - essential planning policy guidance.