PIP Assessment

My son has now been invited to claim PIP from DLA. All forms filled in as detailed as possible, names of Drs and specialists given, and PIP form sent off. He received a letter saying they were writing to the named people on the list for more information. Excellent we thought they will have everything they need from the hospital. I included a few X-rays with the original claim. Now we have received a letter for a face to face assessment with a physiotherapist. Now I'm coming to my point. My son was born with a syndrome which has left him less abled since birth and has attended a children's hospital on a regular basis having had 24 operations to help him. Everything is documented, photos and consultant notes over the past 21 years which they have access too, so why, why, why are they asking him to see a physiotherapist, who probably has not even heard of his syndrome before she was passed his form