Thank you for all your advice. I have planted what I had under glass. I didn't have enough to save some for later. I just hope there was actually some viable seed there.

My brother's near Leicester got to about 2.5m, also a smaller one. He has now moved house, so I can't ask for any self-sown seedlings.

I have a very light sandy pebbly top-soil, so perhaps I shall be lucky, if I actually get some plants.