I wrote this budget wedding blog a while ago so hopefully you'll find a few tips in there.
Some basic stuff: Don't buy flowers from a florist, you can get some gorgeous bunches from a supermarket, including carnations for button holes, which can be up to 80% cheaper than what you'd pay in a florist.
Print out the invites yourself on some embossed card that you can get from any stationery shop. Not only will they be cheaper but more personal too.
Oxfam have a dedicated bridal gown shop with some designer bargains or shop on ebay for pre-loved dresses.
Ask bridesmaids to provide their own dresses and point them in the way of the Tesco range.
Retro pick and mix sweets wrapped in little organza bags tied with a ribbon make wonderful wedding favours.
Buy plain beer and wine glasses, get some glass pens and personalise them as Best Man gifts, bridesmaid gifts etc.
If you google for budget wedding ideas there are loads more. We had a budget wedding and everyone loved it because it was informal, relaxed and cheerful and it actually meant more to us because the whole day was not centred around how much it had all cost, but how much we loved each other.