They look and sound like sycamore to me
Planes and sycamores can look very similar (although they're not related), and just to confuse the issue in the USA London Planes are referred to as Sycamore, and sycamores can be known as false or mock-plane . My Sycamores (Acer pseudoplatanus) are smooth and not peeling, but they're shaded under oaks and not too old. The way to tell them apart is throw a piece through the air, if it flies its a plane.
Like the ispot link Simon, I've several herbaceous plants I'd like to identify which are appearing where we've cleared the brambles.
If it turns out it is a Plane, the timber 'Lacewood' is very attractive and prized by the likes of turners and woodworkers, the fine stippled grain looks like feathers (and used to sell well in my gallery). Sycamore is also valued timber, but a rather subtle cream colour and can develop curious bright blue staining.