Picture posting is enabled for all :)
I pulled what I thought was a self set sycamore from one of my tubs earlier this year to find what was very clearly a walnut that had sprouted. How it got there (squirrels) is anyone's guess... there are no fruiting Walnuts on the allotments as far as I know. It has recovered from the manhandling into a deep pot... but have no idea what to do next..
I understand that all walnut trees produce very good and expensive timber (in time!) but the best fruiting strains are propagated by grafting. Historically owners of large estates were known to plant a row or two of walnut trees to increase the value of the estate for their grandchildren.