Alvin

This is my boy Alvin Stardust, who's huge and 18 and still loves a gallop. At the moment, with a shaggy winter coat, he's also known as the Woolly Mammoth. Seen behind is the very cheeky Flynn, who's 9 and is Mr GB's horse.

We have been out riding today, in brilliant winter sunlight across frosty fields. It's a great way of seeing wildlife, which isn't quite as nervous of horses with people on them as of people on foot. We saw eight deer, got close to a buzzard, and intrigued a vast brown hare with a black tail.

There is nothing I know that's like horse riding for dissolving any anxiety or dullness of spirits and putting a warm lethargic euphoria in its place. After riding the world always seems a good and friendly place and life has its rightness and sweetness restored.

Quite aside from that quasi-transcendent effect, there's so much to enjoy in the moment - and possibly it's the having to live in the moment that's key to the ensuing happiness, I don't know; it seems possible. Today I tried to be conscious of what the components of that happiness were. It wasn't easy to articulate. But there was the intimacy with the horse to enjoy, in grooming and preparing him - here he has spotted that I have polo mints ; the physical enjoyment of the smell and weight of him, his bright eyed intelligence, his funny rascally endearing little ways. The joy of cantering up a slow green hill, the sun on our backs. Blip moments too: the wide sudden prospect of the firth of Forth and its islands; the beauty of a hawthorn hedge, grey green in the low white sunshine; deer pausing to look at us in a photogenic huddle. Recent heavy rain has meant the lower parts of the fields are waterlogged and frozen. We came to a big icy puddle across our usual track, and I could see Alvin considering what to do, choosing his diversion, having a sly glance at me to ensure I was happy with him. When Flynn took off in a canter, Alvin trotted faster and faster, waiting for the nod from me to up the pace, his ears back so he could hear me say the words he wanted - "Go on then".

I love the feeling when I'm on horseback that I have all the power in the world, commanding that half ton of muscle that could take me anywhere I needed to be, and at speed; and simultaneously, am powerless, at the mercy of my horse's whim, and have given myself over to trust.