Two options:
1. Change your region to United States.
- Relatively easy, gets Cortana more quickly.
- Not fine-tuned for the UK, instead targeted at the US. (e.g. US spellings)
2. Enlist in the Preview for Developers and update to 8.1 Update 1
- Official UK release
- other pluses, like folders!
- future updates more quickly! requires some updates though.