I've just come in on this one. My take is somewhat more brutal.

Firstly, if the quality of the video isn't up to "professional" standards then he shouldn't be paid. End of story.

Not understanding the speeches is certainly not professional quality. Him giving you the original footage, in the hope that you can do a better job is the least he should do. If he argues, then for £50 you can take him to the small claims court (part of your County Court).
Since he cocked-up your wedding video, any judge would award damages. The report of this would appear in the local paper and would (hopefully) put off any potential customers.

If he belongs to any professional trade organisation (such as the IOV) then make sure that they know that one of their members isn't doing a satisfactory job.

Be ruthless, he's depriving someone competant of a living and is taking your money without delivering what he promissed.