Tim Kitchin pointed me to Zopa who say

For the first time, people who want to borrow money have a real alternative to going to a bank or other financial institution for their loan.

You'll be able see immediately what market you are likely to be able to borrow from, the money available and the rate offered. If the rate's not right, you can always save your loan request and come back another day to see if it's improved.

You'll be borrowing from other people like you, not a big corporation and you'll be making the exchange what it is. Your decision whether to borrow or not will affect the rates that are offered by lenders.