Surprised this has not been posted yet...maybe it has? I did a search but I couldn't see it!
Anyhoo, go through quidco to snapfish.com and register a new account. Upload 40 pictures and add them to your basket, you get these absolutely free and only have to pay postage which is 99p or you can collect from Jessops for nada. You'll get £3.50 tracked in your quidco within a few hours, so essentially you are getting 40 free prints and £2.51 profit if you pay for delivery or 40 free prints and £3.50 profit if you collect.
I did it in the wee small hours of the morning and already have it tracked and validated in Quidco and an email from Snapfish saying my prints are done and ready for dispatch!