This one works through Quidco. Payday UK are offering £50 cashback via quidco on any loan taken out from them. The smallest loan they do is for £80, which needs to be repaid with 20 quid interest. But the 50 quid cashback minus the 20 quid interest makes it a clean £30 profit!!!
With cashback sites, there's always a risk of cashback not being paid, but I've personally found quidco to be very reliable. Haven't ever had the need to use PayDay Uk though!http://www.paydayuk.co.uk/
I think its a good deal, but use at your own risk!!! :-)