Many thanks for the replies.
It is the marriage of the parents of Mary Jane Bushell that I am trying to find. Mary was born 6/4/1838 in Robert Street, Gravesend, to John Bushell and Ann Shepherd. The Informant on the birth certificate was the "occupier of House, Mary Shepherd", so it is interesting that one of the Maidstone marriage witnesses had the same initial. I don't have any knowledge of a George Leest but its another avenue to try.
It is my Ann Shepherd in the 1851 Census in Limehouse although her place of birth is a mystery. I Cannot find a Teston in Norfolk and although there is a Teston village in the district of Maidstone, I have always assumed that the handwriting looks more like Irstead, which is a village in Norfolk. However, I have tried and failed to find a Christening record in either Norfolk or Kent. Also I have not been able to find any trace of Ann after the 1851 census when she was only 32 years old.
Bob