“I played a lot of sport as a lad and then became an RSPCA inspector aged 20 or 21. When I joined, they moved you all around the country. The job overtook my whole life from the early 1980s until 2010; 30-odd years.
“I didn’t do any exercise during that time and I smoked. I was always a skinny lad but when I got to 45, I started putting the pounds on. And when I got to 54 I thought: “I’ve got to do things for me and not just for work.”
“I saw the marathon on the telly over a number of years and thought I’d like to give it a go, and then forgot about it. Then my wife said to me I had to do something or I’d never forgive myself. She was right.
“I went to my local playing field, and I did a one-minute walk and a one-minute run. I did that three times, for three minutes, came home and it nearly killed me.
“I said to my wife: ‘There’s no way I can run 26 miles, I can’t even run a bloody minute.’ I was quite upset with myself and quite furious.
“But I was determined, so I got a training plan and worked it up to 20 miles, and stuck to it 100 per cent.
“If I had a training run of eight miles I didn’t stop once because I saw that as a failure, but I’m lucky enough that I’ve got the willpower. I did the training over seven months.
“I’ve got an addictive personality and a lot of the people I run with do too. I think it has got to be the trait of a runner: if you haven’t got an addictive personality for running, why would you continue all the time?
“I gave up smoking when I started my training and it was the biggest incentive to stop because running and smoking do not go hand in hand. I was smoking 30 a day.
“I got a charity place for the London Marathon in 2010 through the RSPCA and raised £2,000. One lady gave me £600. The hardest thing about it was the initial training, doing the first quarter hour non-stop. I was so proud of that.
“During the run itself, I had a little walk at 16 miles and then when I got to 20 miles I’d had it, and then I got annoyed with myself. So I took an extra [energy] gel and it got me round.
“I must have walked about two and a half miles out of the last six because I’d had it. It took me five hours and 40 minutes.
“One of my biggest motivations was the thought of having that medal around my neck and once I’d got that, I’d have it for the rest of my life.
“Now running has become a bug, and I’ve done three marathons and 23 half marathons.
“I had my lungs X-rayed four years after the first marathon and the doctor said to me: “Lucky you’ve never smoked”, so that was a real benefit. They appear to have repaired themselves.
“I’m not saying I’m out of the woods because I don’t know what damage I did to myself over those years.
“The first marathon I did I trained on my own, and then the greatest thing I did ever was to join the Burnham Joggers Athletics Club. [The first time] I went I found it one of the most intimidating things in my whole life but I persevered with it.
“I was intimidated because I was thinking: ‘Are all these people fitter and better than me?’ and, second, meeting strangers can be intimidating.
“But now I’d advise anyone to join a beginner’s course in a running club. Not only do you get fit, you will make really good friends. I’ve made what I can only describe as lifetime friends and that’s so important. It’s made me realise that friendship and people are more important than my job.
“Sometimes I come home and worry about things, but when I’m running all my worries seem to go away.
“I’m inspired by the older runners there. Alan is ten years older than me so I think: “I’ve got ten years’ more running in me”, and then I see Tommy, who’s 78, and think, “I’ve got 20 years”.
“I want to be a catalyst, because if I don’t do it, no one else will. I want to organise as many people as possible to do the Benidorm half-marathon.
“Also I like the idea of doing an extreme marathon, something like the Las Vegas [where people run down The Strip at night].
“What I have learned is that there is more to life than work and also I’ve discovered that your world needs people to be a catalyst and say: ‘Let’s do this’.”
Derek Wilkins has raised more than £6,000 for the RSPCA through sponsored runs