What's under YOUR Lawn?

We had good weather yesterday after a day of heavy rain.  It was a perfect time for me to investigate the strange brown patches on our lawn.

Patch is an understatement. One was the size of a miniature aircraft landing strip laid across the grass!

So I dug and dug and guess what I found?  Great sheets of clear polythene about a foot down (don't ask me for the metric, I'm still an old-fashioned girl at heart).

It wasn't a total surprise as we had dug over another area of the garden when we first moved in  three years ago. Then I had found large polythene sacks (also buried at a depth) filled with rubble.  I keep wondering when I'm going to dig up the body!

I've relaid the grass now and removed a section of the offending substance. Whatever purpose did it serve? Maybe you can think of some, because I certainly can't, other than a handy way to dispose of their rubbish.