In message , Bob Hobden
writes
Someone of another Ng has posted a photo of a weed we used to have on a
previous allotment, but do you think I can remember the name!!!
Perennial, too deep rooted to dig out, reddish roots ( we called it Red
Root), hairy/spiny stem to 2 metres, leaves alternate with spines underneath
on the midrib. Possibly with yellow flowers but we never let it flower.

I don't know about the rest, but Lactuca serriola (prickly lettuce) has
spines underneath on the midrib. It does have yellow flowers.
--
Stewart Robert Hinsley