If your project involves building from scratch, an extension over the dimensions specified above or affects an a) listed building, b) property in a AONB or c) home in a conservation area,then Permitted Development rights do not apply, and you will need to make a full planning permission application.
You should always check with your Local Planning Authority, as in some cases Permitted Development rights are restricted or removed under an Article 4 Direction, meaning that full planning permission is required.
By way of an example, if you have a new build or newly converted property and:
You want to raise a Buy-to-Let mortgage;
You’re selling and your buyer needs a mortgage or;
You need to re-mortgage the property and release the property’s equity;
A PCC is widely accepted by lenders as it is backed by the consultant’s professional indemnity insurance, and attest to the structural quality of the dwelling. If you know you're not going to sell in the next six years, then you don't need one - but it pays to be safer than sorry further down the line.