And where do you think all of that run-off goes? Now it contributes to down-stream flooding. If your lawn had been laid properly, with some french drains and a sand layer between the turf and clay, it would have drained just fine. All you have done is passed your problem on to someone else!! Your response actually demonstrates why plastic carpet in your back garden is not a great idea. Its called NIMBY (Not In My Back Yard) for a reason.
thank you for taking the words literally out of my mouth.