It's now less than three days until the London marathon. Over the past two months, my life has completely changed. You know that running bug people talk about? Well I've been well and truly bitten. Whatever happens this weekend – whether I finish or not (I'll be keeping my fingers crossed) – running will now always be a big part of my life.

When asked to join the Evening Standard Dispossessed Fund team by my friend, journalist David Cohen, I tried to come up with an alibi to get me off the hook. But the more I heard about the thousands of people that the charity helped across London, combined with the stick I was getting from my wife Saadiya – I couldn't say no.

That decision was one of the best I've ever made. Because I had left it so late, David put me on a strict training regime. Two short runs into work in the week and a long Sunday morning run. It took a while to get used to such long distances, and the first few left me hobbling around Parliament.

Since it began in 1981, the marathon has become the capital's biggest festival; I'll be joining 35,000 other runners at the start line, cheered on by over 650,000 spectators. It's the largest race and biggest annual fundraising event anywhere in the world, having raised more than £660m to date.

I've had the privilege to visit many of the projects supported by the Dispossessed Fund, which tackles poverty and inequality across London. Knowing the money I raise will go to help even more people is a real motivator. And if all else fails I've got my competitive nature – I'm desperate to beat Ed Balls, who is running his third London marathon.

I never understood how much running changes your life. I'm now obsessed. When not trying to beat my personal best, I'm talking to other people about theirs, reading training advice or eating the perfect balance of carbs and protein. There is a calmness and focus that I've never experienced from anything else. It's done wonders for my physical and psychological health. You might not feel it the first time you lace up your trainers, but trust me, stick with it and it will change your whole life. If you see me on Sunday please shout some encouragement and wish me luck ... I'm going to need it.