walgreens has a free app .... i use there online photo center all the time.... i upload from computer to any of there stores and pick them up or they will send them to you....
but now i look at it, it looks like there app will do that via the iPhone.... so i'll try it out and get back to you..... (i have a walgreens about a mile away from me and i'll give it a go right now)
just search for : walgreens in the store... (don't know how to set up a link to the app store)
EDIT OOOPS: you're in the UK... did see that... sorry