If the DWP refuses your Personal Independence Payment claim or awards you a lower rate than you deserve, the first formal statutory challenge is called a Mandatory Reconsideration (MR).
You must request a Mandatory Reconsideration within one calendar month of the date written on the top of your DWP decision letter. If you have missed this deadline, you can still submit a late request up to 13 months after the decision if you have "good cause" (e.g. hospitalization, severe illness, or postal delays).
Before writing your MR request, call the PIP helpline immediately and request a copy of your PA4 Consultation Report (the report written by the healthcare professional who assessed you). Comparing the PA4 against your original PIP2 questionnaire reveals exactly where the assessor made factual errors or omitted your evidence.
The DWP will issue a Mandatory Reconsideration Notice stating whether they have changed the decision. Only about 15-20% of MRs result in a positive award. However, receiving the MRN gives you the legal right to appeal to the independent First-tier Tribunal, where over 70% of claimants win.