I had a look at my records for Kennington St. Mary, but I can't find a Baptism. I can't find the Marriage either, but I've found the Banns for a William Bourne & Charlotte DOWN (Ashford) banns called 21st, 28th Mar, 4th April 1802.
The Church was St. Mary Kennington.
If that is your William & as Charlotte was from Ashford, it's more likely the marriage took place there.
Betty