It may actually be an overgrown spring onion!
One of two remaining in Raised Bed B since 2020. They didn’t smell particularly oniony which is why I left them to grow on and see what developed (in case it was a purple allium).
Last year, I accidentally pulled this one up while removing some lettuces that had gone over, so I just left it lying on the bed. Since then, it has grown much longer (horizontally) and is now at least two feetl; it formed a flower head, and now has a ‘baby’ growing. All without its roots in the ground.
I’ve put it back on – but not in – the bed for now.