I followed the advice on this website and went to the PIP appeal tribunal today with my son, who received higher level DLA for 13 years but was originally awarded only 4 points for mobility at his initial PIP interview in December. Following MR, he was awarded standard rate mobility. Three panel members, very pleasant, although asking very searching 'hypothetical' questions, e.g.' even though you don't usually use crutches, how far hypothetically do you think you could walk with crutches?' Ultimately, the panel decided that he was entitled to the enhanced rate for mobility and, bizarrely, an unspecified number of points for daily living, which he has never claimed.
My advice is to make sure you pick apart every sentence of the original DM's report and the subsequent MR report and cross reference every anomaly, particularly instance where the DM's report is at variance with consultants' reports.
Thanks to everyone who contributes valuable information to this website.