I awoke earlier this week to the revelation that the government has declared war on me. Is it because of bad writing? No. It's because I'm fat. F.A.T. I really am. I have moved out of denial and into maternity clothes. I'm typing this in my sister's maternity trousers, although I am not with child, but with Minstrel. Last week I sat on a table and it collapsed. It had to be taken back to Ikea for a decent burial. I have begun to get nervous about travelling on the tube, because I spread on to neighbouring seats, where my fat is met with those peculiarly London psycho stares. And now I have been invaded. Gordon Brown's first war is on me. I pray the collateral damage will not be my shoe cupboard - or, worse, the fridge.

The strategy is this. The Whitehall fat police have given £30m - you could buy 15,075,377 Big Macs for that in Britain, or 8,116,808 in Norway - to nine cities in the UK, to instigate measures to shrink the population. Because Brown thinks that if the obesity epidemic isn't halted - I love this term because it makes me think that fatness is contagious, like rabies - the NHS will have a stroke and we will all have to waddle to its grave, like giant weeping balloons. Also, he is concerned that the fatties will embarrass the nation at the Olympics. So, if you make an effort to get smaller, you will get free carrots and tracksuits, and possibly even an onion. If you jog around the park, take a keep-fit class or a weight-loss class (miraculous advice - eat less!) you will get points, which you can spend on yet more slimming activities.

I love the welfare state at times like this. "Please can I get incapacity benefit and a turnip?" "Yes, love, and I'll throw in a cabbage and some size-five sports socks. Good luck!" I don't know if the War on Obesity will work, and neither do the sniggering columnists, who treat the fatties exactly as they did at school: "You're fat! Loser! How dare you take precious tax revenues that should be used to maintain the charitable status of my child's private school?" But it makes me want to write about obesity, partly because when I'm writing I don't have to move.

The most important question is - why am I fat? Why are we fat? Superficially, this is as stupid a question as "How on earth did I get pregnant, Mummy?" I am fat because I eat too much. It's the sugar, dummy. ("It's the sperm, dummy.")

But why do we British eat so much? Is it the sedentary lifestyle, the food deserts - the estates where fresh food hasn't yet been discovered - or the replacement of our playing fields with branches of Nando's? Have chips just got better? And what of me? Do I eat so I can get fat hate? It's possible. I might have a chocolate- themed type of Munchausen's, which allows me to feel important. My parking space on the planet is BIG and yours is SMALL. You can't miss me. There are website pages dedicated to critiques of my thighs and their impact on my emotional state and sex life: "Fat girls tend to be easy ... they have to be." (Thanks!) Once, after I was pictured in a newspaper, a Fat Guru from Teddington rang me at home at 9pm."I'm so sorry you are so fat," she said, like a Little Britain character. "Fuck you," I replied.

I haven't always been fat, reader. I was thin until I became an adult. Did adulthood make me fat?

Perhaps it was a fear of responsibility. I used to have anxiety dreams where I couldn't operate a vacuum cleaner. And by puberty I looked like Mr Greedy from the Mr Men, but slightly more beige and distressed. And then ... I entered the diet vortex. I wish I didn't sound so bitter. Perhaps a Prêt All-Day Breakfast sandwich with extra ketchup will soothe the pain?

I have tried every diet that ever existed. I have done the Hay, the F-Plan and the Atkins. (I didn't know there was so much shit in the world.) I got bigger. So I tried the weird diets with silly names - the French Women Don't Get Fat (But Italian Women Do) diet, the Eat This, Not That, the Fat Smash, the Fast Food, the Hallelujah, the Amputation, the Lemonade and the Russian Airforce.

My favourite was the Jesus diet, which was designed by fundamentalist Christians.

So what can the government possibly do to stop people like me from getting fat? I have some suggestions to help it conduct its war on me. Everyone knows that in weight loss, to get results, you have to go the extra mile. So, bring on the pain. Please can we have forks that give you electric shocks when they sense sugar? I would like to see armed guards patrolling the biscuit aisle at Tesco and I would like to have a personal trainer who comes round every morning to shout, "Why are you so fat?" at me. I would also like a talking spoon and - I found this on the web - an anti-eating mouth cage.

But the dull truth is - I'm ambivalent about being fat. On the one hand, I am weeping fat tears. I hate the public shame of being fat. On the other, I get to eat mini-rolls all the time. And if you're being honest, you want to eat them too. Don't you? Don't you secretly envy me and my fellow fatties? Because we are everything you dream of being? Screw the NHS! And screw Brown. (You're fat too!) I don't tell you not to race cars at high speeds or complain when I have to pay for the ambulance that drives your shattered body to hospital. I don't begrudge paying a helicopter to pick you up from Mount Snowdon because you got lost, you idiot. So you can pay for my heart attack, you bastards. Now, if you will excuse me, I have to go. I'm hungry.

• This week Tanya watched Sewer Baby, an obscure American horror film in which an aborted foetus returns from the dead to terrorise its mommy: "Have you ever seen the sewer baby? Beware, beware of the sewer baby!"