Hi Catherine - think so - only slight hitch here is we don't have an absolute on it being Selby rather than Selwyn!
1840 marriages are typed up on findmypast, and that is clearly Selwyn; really need to see the original of the marriage to be a bit sure, don't you think?
However, gut feeling is yes, it should be Selby - which fits better with the name on Frederick's birth certificate, and explains why there are no Selwyns in Hankerton!