I've always been a decent runner so I've never been massively unfit, but for this I've got stronger. I've got rid of a bit of podge and I'm just a bit leaner, which means that I'm just quicker at moving, I'm more agile and I recover much better as well. At the moment I feel ultra-fit and it's been an amazing change.

At the end of October I started doing a bit more swimming and learning how to swim properly, because I hadn't really done it since I was at school. Then I really accelerated in December and for the whole of January's I've been doing at least one thing a day - normally a swim and a cycle, or a swim and a run, every single day.

I've always been a decent runner so I've never been massively unfit, but for this I've got stronger. I've got rid of a bit of podge and I'm just a bit leaner, which means that I'm just quicker at moving, I'm more agile and I recover much better as well. At the moment I feel ultra-fit and it's been an amazing change.

What's most troubling is the open water swim. It's windy, the waves are getting in your face and the water is a bit dirty. And there's silly things like you can't touch the bottom if you swallow a mouthful of water.

There's going to be a lot of eating. My listeners have tweeted me and said "You've just got to keep eating, keep your energy up and have someone on duty to give you a massage if you need it." It will be a case of getting it done and making sure I don't get too cold, because that's crucial for the muscles. So that's all going to be taken care of. But really there's not much you can do - if you start cramping up you've just got to get on with it.

I just have to deal with it [injuries] if and when problems happen. It's obviously a concern and I've been very careful with my training, making sure I warm up and warm down before everything and not pushing myself too stupidly.

'm starting to get a swimming physique, which I'm very pleased about, because for me that's the most appealing male physique. It's not show-y off-y Mr Muscle, "Look how much I can bench." It's just a real lean, athletic figure and it doesn't look like you try too hard. When you see people who have huge biceps, it looks like they're in the gym all day. But I think there's a difference between looking muscly and being fit.