I came across these recently and was baffled. Each was around 20m long and 1m wide. I later found out that they are from an archeological survey carried out by a property developer before building a new housing estate. He used a digger to scrape through the topsoil to a depth of a few feet to check if there was anything of interest. Thought you might be interested.
I was already on the verge of asking if there was any sign of Tony Robinson and the Time Team gang before reading the full post.