Map showing all locations mentioned on Wikipedia article:
Lower Horse is an
uninhabited island off the English coast, lying
in the Thames
Estuary between Canvey Island and Stanford-le-Hope, close to . Consisting mainly of marshland it is part of the group of islands (five
of which later re-clustered to form Canvey Island) that broke away
from the English coastline in the medieval
period.
Administratively it is part of Thurrock unitary
authority; the border with Essex running
between it and Canvey Island.