Dear MartinWL, Presumably your father is receiving Attendance Allowance. The "severe" element of SMI is often at the discretion of the GP. 127 of the 382 UK councils backdate to the date of GP certification. You are one of the lucky ones.I got the discount for my father without any real difficulty. I had been of the view that his mental impairment was too mild to count as a "severe mental impairment" but decided to enquire of his GP whether he was willing to certify "SMI". The GP was willing and although it took a few weeks I was successful and my father received a refund of council tax paid since diagnosis. So I think this was worth a try.