It's important that athletes can compete on a level playing field. And youngsters coming into the sport can know that if they are working hard and training hard, they'll see a true reflection of where they stand and what they can achieve worldwide and not be swayed by people who are cheating.

I have not had the chance to go out there and do myself justice in an Olympic marathon yet. I have not been able to get to an Olympic marathon injury-free yet.

I would be happy with an Olympic bronze. What I don't have is an Olympic medal.

If you look back at my marathons and ask whether I would swap one of them for my one balls-up, of course I would. But you can't choose. You have to make the best of it on the day.

I have achieved a lot and I'm grateful for that - I'm just a bit greedy because I want to add the Olympics. It's once every four years - everyone wants it and very few people get it.

In the marathon anything can happen.

I've been to three Olympics and I don't feel I've ever quite achieved my best at any of them.