How marbleous!

''It's because they spent their childhood shut up in rooms,'' I said the other day when asked to explain the creativity of such families as the Brontes, Sitwells and Mitfords. Perhaps I wasn't being serious, but there's something in what I said.

In those distant days when there was no television, what was to be done between luncheon and tea? I remember that it was always raining, but there are two quite different English childhoods: the popular letters to The Timesm one, ''Where have all the summers gone?'' and mine, ''It doesn't rain like it used to.''

Those long rainy afternoons had to be used up. I did start a novel at the age of five, but it got lost, so I began another career, designing hats and cars.

Looking at the hats now, I don't think they were too bad. They would have done for Ascot, perhaps, since they not only had to be ''worn'' but some of them would have required several human supporters like those employed by the famous Mrs. Shilling, who arrives most years at Ascot with a separate truck containing her hat. (She was subsequently photographed briefly as she staggered under the monstrous yet splendid creation.)

The cars, I fear, might have quickly developed serious structural faults, being exceedingly long, like airline limousines, but with the wheels in odd places. Maybe, had I continued with my career, I might have had a hand in the creation of the Ford Edsel. Indeed when I saw one of those cars in the fifties I immediately identified with it. It was almost as beautiful as the forty-eight Hudson - the car you ''walked down into.'' All curves and sleekness, rather like a . . . hat.

Meanwhile when I wasn't shut up in my nursery designing, I was examining real cars and the people who went with them. Of course in those days it was easier: cars had decided personalities, as did their owners. Soon I became an expert at matching the two. There was the no-nonsense Austin driver, the benign Stanley, the silly Morris, the outspoken Ford, the smooth Vauxhall and the flashy Hillman Minx.

Once I had to be rescued from my room by ladder, as I had been accidentally locked up. I was three at the time and not very good with latches. This coincided with the arrival of a very beautiful lady in a black glistening Hillman Minx.

''How marvellous,'' she exclaimed about something, getting out of her car. I was in love with the two immediately, for I nursed a passion for marbles and I thought she had said, ''How marbleous.''

I thought I had forgotten all this, but I saw a similar well-preserved Hillman Minx in Richmond Park the other day and my heart trembled. Instinctively I said to myself, ''How marbleous,'' and it all came back: the car , the woman, hats, and of course being shut up in rooms.