Tobster,
I've never used them myself, but I have read some posts on this forum about the pilots warehouse that were less than complimentary. See here for instance.
http://www.pprune.org/private-flying...use-co-uk.html
I'd ask around and check they are ok. I'd also recommend that you buy with a credit card (do you have one as you are 15) and make sure your order is over £100. I've been sting before, and discovered that until you spend that much, protection from buying with credit cards is at the whim of the credit card company, not law.
Good luck. IPZ