SECOND THOUGHTS : Don't tell the cats, but my heart's gone to the dogs

Are you a "cat person" or a "dog person"? The phrase is a clich of no-risk conversation, mindless cocktail party chat, because nearly everyone knows exactly what kind of "person" they are. "Cats ... independent ... inscrutable ... walk by themselves ... keep themselves clean ... huge mysterious intelligence ... Dogs ... dependent ... affectionate ... loyal ... brainless ... big red tongues ... man's best friend ..."

My trouble is that although I'm a cat person and they've owned me all my life, inside there's a dog person barking to get out. Every time Cruft's comes round and the papers are full of pictures of shih-tzus with squashed- up faces, immaculate Airedales with permy curls, intelligent Jack Russells with muscly bottoms, the old dogstrings in my heart are pulled and I wonder whether to get a dog or not.

What is it I want from a dog? I want to be loved, of course, and a dog would dote; I want, also, an outlet for all my longings to look after something. At 21, my son is far too old to need fussing over but, unfortunately, the urge to fuss and care for something small does not die down. And the feelings can live inside, painfully undischarged, like the milk from the mother of a stillborn child. Weekly I watch Animal Hospital on television and weekly I'm tempted to ring up the clinic and adopt absolutely everything, from the ferret to the rabbit to the pitifully maltreated poodle whose recovery is charted every week.

Every time I walk in the park I crave a four-legged friend, straining at the leash, eventually leaping off to race ahead, race back, tell me the news, race away again. I long to have a dog sitting next to me in the front of the car, panting with excitement, eyes bulging with astonishment and interest at every movement in the street. I long to put down a bowl of food and, instead of witnessing the icy disdain of the cats, who regard with bored dismay everything from Whiskas to Gourmet, hear the chop- licking sound of a dog with a hearty appetite wolfing down every scrap.

But the strong emotional longing is tempered by reality, for we have cats. Could a dog ever become a cat person? Could a cat ever become a dog person? One of our cats is crazed and toothless, a frightened, bony creature with mad eyes. It would not be kind to let a foul-breathed, barking hound ruin the last days of his life.

Anyway, we live in London. And in tests, when asked, nine out of 10 dogs would prefer not to live in London. They don't wish to get into a car and be driven in heavy traffic to the park once a day, nor do they want to be walked round a concrete block. A dog would not like to spend the vast majority of his day lying in the room where I work, staring at me goggling at a word processor. No, a dog would like to spend his day roaming the open fields, chasing butterflies, stalking bees, haring after rabbits, leaping into rivers and rolling in cowpats.

And although I know that a dog is not just for Christmas, what worries me is that a dog is for Christmas, and Christmas next year, too. And the year after that. A dog is for Christmas and Christmas and Christmas and Christmas - and Christmas and Christmas and Christmas. There is no way that I could take on a dog and then, if I didn't like it, give it away. In my time I've given boyfriends the heave-ho; I could never live with myself if I did the same to a dog, however badly behaved it was.

Sometimes I wish I could have a dog on loan for three months; I've even toyed with the idea of going to Battersea Dogs' Home and asking for a dog with cancer, a pet with a death sentence, so that I could give a dog a four-month trial. But for some reason no one at home is very keen on that idea. And anyway, I don't know how I could face Battersea Dogs' Home, which houses shed after shed of unwanted dogs in concrete pens, all screaming to be taken home with you.

I question, too, whether for the next 10 or so years I could really find the time to give a dog two long walks a day, which is what it needs. And I know that, being pack animals, a dog is never completely happy on its own. Nearly all animals, from goldfish to horses, should, in an ideal world, be acquired in pairs.

And so I console myself with the phrase: "When we move to the country", and wonder how many potential dog-owners must harbour similar rural fantasies. In the meantime, two cats, several thousand fleas, a hedgehog who hasn't been seen for six months and a birdtable squawking with birds will have to satisfy my pet-loving urges.

Oh, and a pond full of frog-spawn. Last week I drove across London with a bucket of the stuff from a friend's pond, hoping to found a new colony in Shepherd's Bush. The only trouble with frogs is that you can't take them for walks.