There are a number of mentions of sorrel in the what I am growing section. I have dock coming up all over the garden it is enemy no 3, can I eat it?
I am sure it would not grow so strongly if it knew I was going to eat it.
I wouldn't advocate eating/cultivating dock! It's got many herbal/medicinal uses but as far as it goes as an allotment 'companion' you're best rid. Especially when it goes to seed!
There is a record of a dock seed being found in an Egyptian tomb. Thousands of years old and it STILL germinated!
Dig the b***gers out as best you can and NEVER EVER put the roots in your compost.
Sorrel is another question? I love the stuff and plant it in pots to contain it.