The first thing I do when I wake up is look at the tree I'm under. It's a tree of bold contrasts - like me, I suppose. I have bipolar disorder. It's a disability that messes with things like my emotions, memory, concentration and co-ordination. It makes normal life pretty much impossible - it's why I'm homeless. If I had my own home, it would be like walking a tightrope all the time. I'd panic, I'd keep falling off, because I wouldn't be able to cope.

Mornings are often terrible - I can wake up crying for no reason. But I still get up and like to look smart. I put on my Versace shirt, my silk tie, my jet cuff links and my navy suit. I even have a Christian Dior coat - all hand-outs. I put them on a hanger on a tree. After I've brushed my teeth and polished my shoes, I roll up my sleeping bag and groundsheet and stick them and my pyjamas into a holdall. I also have a briefcase for all my paperwork.

Living this way has its restrictions, not least being the lack of a handy loo to run to. But, hey, you adapt. I live day to day by using the services that are either free, like public lavatories and libraries, or that cater for homeless people.

The day centres and drop-ins are run by churches and charities and, on one level, provide everything: breakfast, showers, haircuts, razors, shampoo, clothes, pedicures, doctors and free transport. I even have an 'office', because these places also provide access to computers, printers, discs, the internet... I'm on e-mail and I've set up my own website!

It was this day-centre network that enabled me to write my book, The Hidden Code of Cryptic Crosswords. I wrote it because I couldn't make sense of cryptic clues and ended up becoming obsessed with them. It took five years. I actually started it before I was diagnosed with bipolar. I realised I had it following a breakdown - I just wandered out into four lanes of traffic one day, and I couldn't speak or move. Luckily, a friend found me and took me to his home. A few days later I went to a psychiatric hospital, where my mental illness was diagnosed and I was prescribed lithium tablets. They keep the extremes of bipolar at bay.

I was also assigned a psychiatrist, who I still see every three months. That's all the support structure I have.
I can now see I'd shown many of the warning signs. My behaviour was often erratic. I was moody, I couldn't concentrate. I was slow at school and had huge problems with exams. I must have had 25 jobs by my early twenties.

My family and friends didn't suspect anything, because I guess they didn't know what they were looking for.

The bipolar disorder boils down to an imbalance of chemicals in my brain. It results in a whole cocktail of symptoms. Manic-depression is one of the more recognisable sides to it. Sometimes I'm so full of despair and darkness, I don't want to live any more. But other times, I get ecstatic about the smallest thing. When I'm like that, I'm usually loquacious and fluent and want to stay up all night chatting. Other times, my ability to communicate falls apart and I find it impossible to speak at all. A lot of bipolar people turn to excessive drink and drugs or other forms of self-harm to escape all their fears. Apparently, if untreated, one in five commit suicide.

Initially I kept my disability in the closet, and I offended people and lost friends. Now my friends know, and if I behave outrageously they still love me. When I have a little bit of money, as I did from my book sales, I just want to spend it all at once. I like to splash out on things like tea at the Ritz. Most of the time, though, I rely on day centres and soup kitchens for meals.

By 6pm, most of the day-centre facilities close. I often end up at a late-night internet cafe. I work hard to be successful and I'm in the middle of writing another book. I know that homelessness does not mean failure and my disability does not make me useless: it just makes me different. A lot of the homeless people I meet have mental illnesses and other hidden disabilities. We only live the way we do because, despite the huge amount of money spent on homelessness today, it's rarely spent on tackling our disabilities. Charities got the blind off the streets by addressing their disability, not their hunger or poverty. Why can't they do the same for us? Are our problems any less important just because you don't see them?

Around midnight I might head back to my tree. Another favourite spot is a gantry along the Thames. It's a beautiful place, where the lights dance on the water and the stars shine down on my face. Some time ago, I found a charity shop that had pyjamas and thought: "What the heck? I'll buy them." If you're going to be eccentric, there's no point in sleeping under the stars in a good suit, is there?