I've often been asked how Poems on the Underground began.

It was hardly an original idea, of course. Sixty years ago, verses about the Thames were inscribed in the pavement between Westminster and Waterloo Bridges for the Festival of Britain. A 'Magazine of the Arts' flourished briefly on buses in New York (my home town), decorative panels of art and poetry filling empty advertising spaces.

Yet our own project struck a special chord with the public. We're now world-famous as a form of public art, known and loved by thousands, imitated in cities across the world. As we enter our 26th year, it's time to tell the truth.

I must go back more than 35 years to my first encounter with London literary life, when my husband and I lived in the North London house of Adrian and Celia Mitchell, the left-wing poet and playwright and his actress wife. Adrian was supposed to be enjoying the quiet of Yorkshire, but an assignment as TV reviewer took him back to London, and he rented back his study cum bedroom for one day a week.

On the other six days I used the room as my own study, removing my papers when Adrian phoned to say he was coming down.He worked harder than anyone I knew. I would hear his Olivetti pounding away upstairs while I sat, blocked, at my new Hermes, a floor below. An atrocity would be reported in the press, a child ...