Hi Paul Sounds like you need to put some land drainage in . These are trenches that are lined with membrane . You then lay perforated pipe surrounded with shingle into them. The pipe is connected to either existing storm water drainage or a soak away . Soak aways in clay are tricky as they need to go deep enough to hit some free draining ground. You would also have to either dig out the top layer of your current lawn and replace with some free draining soil ( add some sharp sand to the topsoil will help) if your not governed by any levels then consider just raising your lawn level slightly .