For anyone wondering about the name Leasowes, it apparently means pasture land/feeding grounds.
There is a large area in the Wirral called Leasowes.
I am still trying to follow the William Foster link. As far as I can tell his widow lived on at Mel Valley until her death in 1944 but the contents of the Mel Valley stud seem to have been auctioned off in 1914 soon after William's death. I have also found a reference in October 1915 in the Birmingham Mail to "Moseley Volunteer Training Corps" meeting at "New Ground, Windermere Road". I wonder if this is the ground we are looking at now?