I asked the Irish Phone providers about details in regards to unlocking the bootloader on the Xperia Z. So far, only Eircom (eMobile) got back to me - Since they and Metor are basically the same company by now, I think it holds true for them too:
eMobile Ireland:
@MeisterLiTweet Hi MeisterLiTweet, Unfortunately it is not possible to sell a Xperia Z with an unlockable bootloader. Grainne
eMobile Ireland:
@MeisterLiTweet Hi MeisterLiTweet, Unfortunately it is not possible to sell a Xperia Z with an unlockable bootloader. Grainne