I did it! I ran all the way! The first mile took under 10mins so I am told this makes me a runner, but for the rest I was slower. It was raining so I got soaked but it didn't bother me once out running. The second mile I found the hardest; my legs felt heavy and I thought I was going to have to walk, but by the third mile my legs got lighter and I was able to manage to put in a (very short) spurt to reach the finish in 32:03mins which I was pleased with. It's entirely due to my companion that I didn't give up, and I'm so grateful to her for talking me through the 2nd half.
I got an e-mail saying I was 2nd in my age category, but when I viewed the results there were only 2 in it! At least I wasn't last, in fact I was 132nd/181. I felt sick half way round but am feeling better now that I've eaten and rested. I was able to wander round Taunton shops for the rest of the day and am leading a 10k charity walk tomorrow so my recovery time must have benefitted from the training long term although my running time has plateau-ed. I think I may have agreed to do it again now - caught in a weak moment!
I posted that I had lost the plot a few days before doing the parkrun. I really didn't think I could do it. Thanks for all the replies and advice from other C25k runners in this community.