Buy some expensive wine for the beginning of the night, and fill the empty bottles with cheap stuff!!After a few drinks they won't realise that they are all drinking cheap plonk!!
Try looking at the supermarket magazines like the Somerfield or Tesco ones. They often have a write up on wines they have in stock and suggestions of which wine would go with which food. The supermarkets often have good deals on 3 or 4 bottles for £10 and also 5% off when you buy 6 or more bottles. Who is to know if its a good wine or not anyway, so long as you like the taste.
If you can, hire/borrow a van go to Tesco Wine in Calais (yep, it's just full of cheap wine) and you will get wine much cheaper than over here, even in the same Tesco stores.
You can taste all the wines you want to buy too. I say most wines are 50% cheaper.
If you bring with you your marriage certificate, an invitation and seating plan to prove it's for a wedding customs can't stop you.