Consultant letter following appointment

Hello there, Following a recent hospital stay I was referred on for a neurosurgeon's opinion. At the appointment I was in my wheelchair. Although he took details of my previous medical history (my normal medical history file was not there) he undertook cursory physical testing of certain muscles. He did not ask me to stand from the wheelchair, see me walk etc. However I have now received a copy of a letter sent to my GP in which states I am able to walk 10-25 yards unaided. He asked me a question about distance I can walk and I replied 10-15 yards. He never asked about me if my walking was aided or not. He also goes on about the weakness of both lower and upper limbs but then scores me as almost normal strength of these limbs. He also states that I sorted through a collection of medical notes (two pieces of paper) and could undo and do up a zip. My coat was removed by my husband in the waiting room as it was so warm and although it has a zip it has large buttons and on a flap and I never use the zip to fasten that or any other coat.

My question is how can I get the inaccuracies in this letter corrected, bearing in mind that this will be on my GP file and also the hospital records for the DWP to see in the future and could be more recent than other medical evidence that contradicts this. Sorry for the ramble.