Thanks Climbgirl!
I was googling yesterday and found one place that *rented* dresses from £695!!! What on earth?! I had a big, white, poofy wedding dress, and it cost £700 to buy! I guess maybe they can't get many wears out of it, so it's not as economical as say, hiring a dinner suit.
David's Bridal is a great shout, thank you. I had a flower girl dress bought by an American relative over there because the choice was so vast. I didn't know they had one here so I will definitely mention it.