The tree was young so no seeds but the bark was definitely platanus and the leaves were huge. much bigger than platanus x acerifolia.
SOLVED: which platanus
Well, you can look into P. racemosa, the California Sycamore. It has deeply cut leaves like that, but not usually that toothed pattern on the margin. Not impossible, though.
Another option is P. x acerifolia, growing under lush conditions that mean larger leaves.
Are you sure it is Sycamore? Alternate leaves? It also looks like a maple (Which is where P. x acer... ifolia gets its name)
hmmm maybe it was just a well fed London plane. Thanks