After an expensive disaster with the two avenues of yews that initially ran down either side of the lawn and drowned in the waterlogged soil, we decided on the much tougher carpinus betulus (hornbeam) on the basis that this is a plant that can tolerate wet feet. We sourced the large specimen trees- fastigiate, pleached and cylindrical- as well as planting hedges where the yew had once stood. Even then, the hedging whips and trees endured a tough few years establishing themselves in the inhospitable soil conditions; indeed, it was fully five years before all the plants filled out and began to thrive.
As for the lawn itself, moss continues to thrive in the wet conditions and, although a central drain was installed to help alleviate the problem of standing water in periods of heavy rainfall, more land drains are needed in the future as well as a regular programme of moss killing lawn treatment, scarification, dethatching and top dressing. Hopefully, one day we will win the battle.......!