Nexus 5 from UK retail

So I'm finally joining the nexus warriors' ranks #holoyolo. My mother is traveling soon to the UK ans she'll buy it from there. The problem is she won't be staying long and doesn't have much technological expertise so Google Play isn't an option for her. I suggested retail and she agreed if I can find it in the same (cheap) price range. I also want to get a good case for it as I have a horrible tendency of letting my phone fall and the SPIGEN Neo Hybrid looks awesome. My questions are:

- Is there a way to get the Nexus 5 32 GB unlocked from retail (I only found it locked on O2)?
- If not, is there a place cheaper than Carphone Warehouse (329 VAT free)?
- Which shops (preferably on Oxford street) sell good cases that I can check online?

Thanks for your help!