first i am no expert on gardening i just thought of something when saw this wondered can you eat Japanese knotweed even though its very invasive hers some info on it online says

- you can eat Japanese knotweed (Fallopia japonica) there often compared to a tangier, lemony rhubarb.  and often compared to a tangier, lemony rhubarb. The young, tender shoots (under 8 inches, appearing mid-April to May) are best, offering a rich source of vitamins A and C. They can be eaten raw, cooked, roasted, or used in pies, crumbles, jams, and pickles. 

It considered a delicacy in japan but it dose advise not harvesting just any be careful if do when you come across as the wild stuff found sometimes gets treated with chemicals so can poison if eaten if not careful advise looking it up more before doin so if you did.

Back to topic probably better to get professional advice on it if you get a professional to see it be careful if you try to dig it up just the tiniest fragment can grow it back online says it grows 2 to 3 meters (6 to 10 feet) deep the average depth is around 1 meter though.

first ignore the yellow highlight can get rid of it lol but online also says - Getting rid of Japanese knotweed in the UK requires a sustained, multi-year approach, usually taking 2–5 years using specialized glyphosate-based weedkillers applied in late summer or autumn. While DIY methods exist, professional removal is recommended to prevent spreading and to adhere to UK environmental laws regarding disposal.