On Friday I met Ben Wilson, the chewing gum man. If you have been to the Tate Modern, you may have seen his work. Not in the museum, but on the Millennium Bridge. The most perfect little paintings on the tiniest pieces of gum.

I saw him as I walked over the bridge, crouched down, painting and then as I approached, he stood up, so I stopped and asked ‘Do you paint these chewing gum paintings?’ He laughed and told me how he liked to paint on the pieces of thrown-away gum. I had often walked across the bridge with my daughter and we had wondered who was behind these perfect pieces of art, so I was delighted to meet him. He was so unassuming. So charming and likeable. We shook hands and went our ways.

I am not a great fan of people who discard their gum by chucking it on the pavement, but if ever there was a good way of dealing with these tiny grey blobs, painting images comes high on the list. This is the purest form of public art. It is underfoot and so doesn’t last long. It is art for the observant, for the curious. We have to pay attention to see it.