Have you looked on the Family Search (free) site? This gives census records as well as BMD records and there seem to have been several David Culys around Wisbech, possibly fathers and sons. I think your David could have married Mary (Ann) Walker 1888, who was much younger than him, but possibly a widow, as some of the children named in the 1891 census were born before the 1888 marriage.
In the 1881 census David is a widowed butcher boarding with Stoker family, who coincidentally have a 2 year old daughter called Mary Ann.
In the 1891 census Mary Culy is 37 and David is a 60 year old butcher. living in Wisbech with children Arthur 7, Ethel 5, Julia 2 and David 1.
The name David seems to have been passed down over generations in this family, as in the 1911 census David junior is now 21 and is a wood sawyer, son of the widowed Mary Ann, shopkeeper.
I can't find a first marriage for David senior, but there's nothing from the start of registration in 1837.
I hope I'm not leading you astray with these remarks, but you can take a look at the Family Search and FreeBMD sites - "free" is the word for both of these!
