With the commercial VoIP service there are two parts you need to consider: Your number(s) and your minutes. You need at least one number, however unlike the residential packages that only permit one number per account, with the commercial service you can have as many numbers as you want. The more you rent, the lower the “per number” cost is.
Once you have purchased your number(s) you can choose your actual number from those available. All UK numbers Geo or Non-Geo cost the same to rent, starting at £2 + VAT per month for one number.