I have already written about a planning application. Do I need to write again, or will my original letter(s) be forwarded?

Provided you have written an individual letter about the application that is the subject of the appeal your letter would be forwarded. 

However, letters related to similar previous applications on the same site that are not the subject of the appeal would not be forwarded.

If you want to double check that your original letter has indeed been received by the Planning Inspectorate you should phone them on 0117 372 632.