From the beginning, I submitted a support ticket to Apple requesting that they give UK customers poster size prints. I heard nothing back so I moved on to Kodak and their UK ofoto service. Ofoto also reported that they didn't offer poster sized prints to UK customers and made no other offers to appease me. I quickly moved on to Snapfish who seemed to be unable to handle the 30meg jpeg which I needed to upload. Various browsers were used (I even tried it from a friends XP machine to no avail) before I finally gave up. I was looking around the other day when I discovered PhotoBox. I didn't think that it would be possible but i signed up for a try. The upload page was a java applet with some very dodgy programming. It didn't work for me. I was about to give up until I noticed that they permitted alternative methods to send photos. MMS, FTP, and email. Clicking the link for ftp brought up a nice finder window for me to send my poster to. 10 minutes later and I have a full quality image on their server. And the rest is purely lovely.
Oh and £20.49 ain't bad. And I know what to get for birthday presents now.