I'm a photographer but non vat registered so cannot help in detail, but we are talking about some fairly small sums here To be vat registered I will assume you are paying £1000 plus for the wedding thats only a £25 difference tax.
As has been said its down to your photographer how he handles this - He may just absorb the difference in price himself, you may have a clause in your contract to cover this ?
Either way you need to be happy before your wedding day