Charlie
Yes, send the evidence with a covering letter to the DWP office dealing with your claim, the address should be on the letter inviting you to claim PIP, you can mark it for the attention of the Decision Maker.
Whilst the DWP should forward it on to the Assessment Provider, I would still take a copy with you to the assessment and ask the assessor to read it and include it in your file before they commence the interview.
Gordon
Nothing on this board constitutes legal advice - always consult a professional about specific problems 
