Well I sortof chickened out. I went down tot he town center this afternoon and enquired again, this time in person. The guy told me the same thing he had told my sister, that it would cost £21 to debrand it and that may or may not unlock it, he also said it would be an additional £15 for unlocking. So I asked him how certain he was that the debranding would also unlock it, he said he wasnt sure at all as it worked on most older phones but some of the more recent phones they had done didnt work.
Since he wasnt sure he phoned his boss who confirmed that it wouldnt work but offered me both for £21 wich I thought was pretty sweet
works out to £10.50 each wich I dont think is all that bad a price since unlocking codes seem to be about £10-£15 on thier own and to do a DIY flash would cost me about £11 minimum.