I apologize, I had checked the wrong user profile to check if you had eCart already. If you have eCart, you will be able to more easily modify the existing PowerStore to use GB Pounds. Otherwise you will have to manually edit several different places to be GB Pounds instead of US Dollars.
As far as the look and feel of the PowerStore, we do not currently have any skins for v2 out, but we are working on them and hope to get them out in the near future. Currently you will need to modify the CSS to match your site layout.