For months now I’ve been jogging around, trying to look like a runner and planning for the distant day when I would have to run a half-marathon. 

It was always the storm on the horizon, the problem that was looming but never arriving. 

But now the rain is about to lash down, and the storm is above my head. This weekend is running time. 

At 9am on Sunday, I’ll be setting off on a 13.1-mile course around the middle of London, pounding through Hyde, Green and St James’ parks, all in an effort to raise a bit of money for charity and prove to myself I really can achieve this curious challenge.

There will be plenty reading this, of course, who will scoff at the idea a half-marathon is any sort of big deal. 

There are ultra-marathon athletes out there who would happily run 13 miles to buy a macrobiotic salad and there are lots of people who’ve been this way ahead of me, pounding streets and counting down the distance. 

But, to paraphrase Ron Burgundy, for me it’s kind of a big deal. 

I used to run a bit at school, but then football came along and running took a back seat. 

Only about 16 months ago did I start taking it in any way seriously, and then, earlier this year, I decided to put my name down for this particular half-marathon. 

At the time, it seemed a really good idea, like putting your name down to join a climb up a mountain.

Then the day comes, you look up and wonder why you agreed. 

No, no, no. I need to think positively. And honestly, I do. I’ve trained, bought proper running shoes, built a playlist of cheesy pop songs and even come up with a target time. 

I’ve got sponsorship (more welcome - just Google adam parsons VirginGiving and you’ll be there) and I’ve even been sent one of those charity running vests where I can iron on my name. 

And I’ve read about running. Not in a constructive way, you understand, but in a typical internet-era scattergun mash of websites and forums and Twitter comments that all coagulate in my mind to make me think I’m an expert. 

I’m no such thing, of course, but I’ve assimilated so many people’s posts I feel I’ve been among friends. 

The golden rule, the one everyone repeats like a holy mantra is not to go off too fast and not to suddenly change a successful routine. 

So when I took part in the Moor Park 10k a couple of weeks back, I was determined to stick to that. Determined, you understand. 

So determined, in fact, I managed to make a succession of ruinous errors. 

Number one - it was ridiculously hot, which I suppose wasn’t my fault. 

Number two - I changed the settings on the running app on my phone just before the start, thereby preventing it from working. After months of allowing my phone to tell me how fast to run, I had cleverly ruined that vital emotional crutch.

Number three - I went off far too fast. Yes the single most important, most obvious and most oft-repeated rule was the one I ignored. Like some kind of puppy, I found myself running at the same pace as the people around me, only to discover they were proper athletes with running club vests. It was only after 3km that I slowed down, not least because I was already feeling knackered. And handily enough...

Number four - that was the very point when we started the 2km long hill that makes the Moor Park race such a fun event. If I had any energy left, it disappeared soon after as I wheezed and coughed my way through the gold course. 

Number five - at least I had my playlist to keep me company. Or at least I did until I poured half a cup of water over my head, only for the liquid to seep into the headphone socket and almost turn everything off. Not the word almost - silence is one thing, but the occasional distant crackle of music is much, much more irritating. 

There were other minor irritations. My number wasn’t on straight, which shouldn’t have annoyed me, but did. 

I briefly felt fine after about 7km, only to gulp down half a glass of water and immediately feel bizarrely unwell, as if a mouthful of water could suddenly give you indigestion. 

I remember once feeling bemused when Mo Farah said he needed to practice how to deal with taking water from a drinks station. Turns out Mo had a point. 

The good news was I did get to the end, rather quicker than I had done the previous year and I’ve learned lessons. 

My phone will now be strapped to my arm within a contraption that looks like one of those things they use to take your blood pressure. 

I’ve bought some waterproof headphones and given myself a good talking to about not going out too fast. 

I’ve even got the prospect of being watched this time, with the family likely to mobilise up to London to take in the event, enjoy the atmosphere and offer some encouragement. 

The charity I’m running for intends to have a "family and friends" gathering area at the 11-mile mark, which is the point of the race when I’m expecting to be red-faced, footsore and probably rather in need of some cheering on. What my children will make of seeing me staggering along like a punch-drunk heavyweight remains to be seen. 

I have to finish, of course. The National Autistic Society is rather counting on it and my pride won’t let me fail. But my two main targets are, firstly, to come home in under two hours and, secondly, to avoid being beaten by a significant number of people in fancy dress. 

Having been passed in last year’s Moor Park 10k by a man who was on the phone making a dinner reservation, I would take it rather personally if I’ve progressed only as far as being outpaced by a bloke dressed as a banana. 

So wish me luck and cross your fingers for cool, dry weather on Sunday morning. This is the first time in my life I’ve ever run this far, and I am (don’t tell anyone) just a little bit nervous.