About five months ago, I started volunteering for a local charity. I did not just wake up one morning and think: I must now do Good Works. It all happened quite organically.

Three miles up the road from me is a remarkable organisation called HorseBack UK. I have mentioned it here before, but it bears repeating. It does the rather amazing thing of using horses to rehabilitate wounded servicemen and women. It works with people who have everything from double amputation to acute post-traumatic stress. I run out of adjectives when I think of what it is they do there. I want to shout and hang out flags. They are absolutely bloody brilliant.

A veteran working with one of the American Quarter HorsesA veteran working with one of the American Quarter Horses

I met the people who set up the charity, quite by chance. I liked them; I was interested in what they did. I went along to visit. I started thinking that just sending a donation was not enough. I wanted to do something. I know a bit about horses, but they did not really need that sort of help. In the end, I offered them the one thing I can do, which is words.

It turned out, by happy chance, that they really did need words. They have to do grant proposals, produce promotional and informative literature, develop a website, and a myriad of other things that require sentences to go with them. Oh yes, I said, not a problem; of course I can do that.

The law of unintended consequences is something in which I have an enduring interest. This blithe offer had two, for me. One is that it turned into easily the most challenging writing I’ve ever done. It’s one thing writing a book or doing a blog or producing an article, in your own name. That is just about personal success; I’m afraid to say it is almost all ego. It’s quite another to produce words for an organisation which touches the actual lives of actual people.

If I get the words right, they may translate into cash, for a new project or a further programme, which may have a material effect on a person who has been blown up by an improvised explosive device. This is a very serious thing indeed, and I frown and struggle and squint over each sentence; each phrase really matters.

The second consequence is that I have become obsessed. I am in danger of becoming a charity bore. I understand now why there are those people who devote their whole lives to guide dogs or the RSPB or Amnesty International. I am like those old ladies in Agatha Christie, who are always going round the village asking for subscriptions for the church roof fund. I think about HorseBack all the time; everything else seems a tiny bit insubstantial by comparison.

It may also be my time of life. As I motor into middle age, I am falling into the platitude of wondering what it’s all about. Time is rushing past me, and I must decide what mark I wish to leave on the world. I’m not a Nobel Laureate or a stateswoman, so it will only be a tiny scratch. But I’d like it to be a good scratch.

Last year’s plan was to plant a lot of trees. I thought that would do. Someone, years after I had gone, would sit under the shade of a rowan or a beech I had planted, and take their ease. I loved the idea of that. Now I think, there is this other thing, that will mean something.

Charity is an interesting paradox. Giving to one or helping one is seen as an act of generosity or altruism. In my case, I cannot claim goodness or selflessness at all. Quite the opposite. It is they who are giving something to me. I get to feel as if I am doing something that counts a bit, even if it is only in my very small way. I get the glorious gift of feeling that my days are not wasted. And that, it turns out, is worth more than diamonds.