Hi tillyboo
We have heard from a number of members who have told us that they have received PIP letter informing them not to enclose a GP letter, my advise is to ignore the request, if you have a very supporting Dr then include their letter as they will know how your condition affects you.
Use extra pages to explain yourself, make sure you number the pages .. page 3 of 7 and write your name and NINO on each page.
Gary
Nothing on this board constitutes legal advice - always consult a professional about specific problems