If you're about to claim PIP for the first time, or you're hoping to renew soon, there are two things that could really help.
First, contact your local CAB and talk to someone there about getting help to fill in the form, then while you're waiting for your appointment to roll around, take a look at this page that Pip approved last night
https://www.citizensadvice.org.uk/Global/Migrated_Documents/adviceguide/pip-9-table-of-activities-descriptors-and-points.pdf and write down what you are like on your worst days using the points on that page in a text document, then print it off and take it with you to the CAB appointment so that you are fully prepared for each question you'll be asked.
In theory, I scored 39 points in Daily Living and 22 points in Mobility so I'm hoping I'll be awarded the enhanced/higher rate in both but I'm not counting my chickens until I've got the decision written down in front of me. If, like me last year, you are turned down initially, definitely ask for a mandatory reconsideration and take it to tribunal so that they can see how you're affected. I didn't go to the tribunal so was only awarded basic daily living last year, totally alone, so hopefully now that I've got the support of the CAB behind me this time I'll be awarded at least the basic on both this time.
Good luck and go get 'em!
