Sorry for the delay, but I had a bit of difficulty pinning it down. I think I got it at January 2013.
I'll contact Siemens, but I don't think I'll get very far - I don't think I filled in the warranty form I got with the machine when I bought it. I'm a bit of a twat about things like that. On top of that, I don't remember the name of the company I bought it from, so I can't even ask them for proof of when I purchased it! Ain't that clever! I think you'll probably hear from me again shortly.
Many thanks for your help,