Black tie? At a wedding? Oh my dear Lord, no.
Morning dress as standard. White tie at a pinch, if it's a late kick off. But black tie at a wedding? Next thing you'll have the bride and groom going away in a pink stretch Hummer.
If you feel you must fit in with the oiks (I would turn up in Morning Dress regardless), then I can recommend buying ex-hire from Lipmans in That London's Famous London. Good kit, very well priced.