I was an English teacher in the Far East for three years, in Taiwan, Tokyo and Shanghai. After a day’s teaching in Taipei in Taiwan, I came home and was flicking through the TV channels and I stumbled across this film that changed my future.

It was about Terry Fox, a Canadian who ran a marathon a day to raise money for cancer research, despite having a leg amputated and running with a prosthetic leg. This moved me so much that I wanted to do what I could for cancer research, especially as I had lost both my grandfathers to cancer. Running was a passion for me and I had run a few marathons before, but watching the film put the idea into my head of running consecutive marathons.

It led me to think about running around Taiwan, so in 2008 I ran 30 marathons around the country in 30 days. The first two weeks were very tough as my body adapted, but the more you push your body the fitter it becomes. But when I finished my 30th marathon I felt quite depressed. Mentally, it was very difficult to stop because my body felt so good and I felt I could do a lot more.

I wanted to do a bigger island and Great Britain fitted the bill. I knew the world record for consecutive marathons was 52 and my aim was to double that.

It took two years to plan, but last September I set off from Brighton. I had a great support team - I wouldn’t have done it without my friends Sam Aynsley and Rick Alleyne - and I used a satellite watch to measure the distance. Wherever I finished, I laid down a marker and then started from there the next day.

It was tough at times. I had a bad injury, a sharp pain in my left shin that took about two weeks to go away and I just had to run through it. But as long as I went at a slow pace, at no point did I think I couldn’t do it. It was a case of persevering and showing determination.

Some marathons took seven hours or more, but the more you push your body the more it adapts. My fastest - about four-and-a-half hours - was marathon 100.

I planned a route right around Britain. The Highlands were a great test - a very barren landscape, no cars and no people, and I was going up and down mountains. But the scenery was wonderful.

There were some wonderful sights. I remember John O’Groats, running down country lanes to reach Land’s End, and running past Loch Ness. It was a fantastic time in my life.

The last month was an absolute joy to run. I woke up and there was no stiffness, my legs felt quite fresh. Your body becomes what you do. That showed me that anything was possible.

I finished my 105th marathon back in Brighton. I had prepared myself mentally: 105 days was the aim I set and I was so pleased to achieve it. I knew there was a possibility for a lot more, but it was the right time to stop. I felt absolutely fantastic.

I learned there are no limits to what I can run. Conceivably, I could run a marathon every day for the rest of my life. Your body adapts and running 26 miles becomes part of your routine.

The record didn’t last long, though. A Belgian man has since completed 365 marathons in 365 days, but I don’t mind. We raised over #163;12,400 for Cancer Research UK, and the money is still coming in.

I’m entering a few ultimate marathon events, 50km and 100km races. One is 250 miles over 100 hours. Ultimate marathons are the logical next step.

I loved my time teaching abroad as well, so I’ve got a place to do a secondary science PGCE. I’m looking forward to that challenge in September.

Neil O’Maonaigh-Lennon was talking to Nick Morrison. To donate, go to www.marathonmad105.com. If you have an experience to share, email features@tes.co.uk.