Hi Matt, it was good to meet and I am pleased you enjoyed the course.
The sorrel is "Buckler leaved". Grows reluctantly from seed, prefers to self seed, or find a bit of root.
As for composting by councils, at least one can say that big strides have been made in the last 15-20 years to make lots of compost, where it was all put into landfill before. Perhaps if it is profitable enough, more materials can be composted: I was looking at the road verges here and am tempted to run the mower out there for a barrowful of greenery, time permitting.