Free migration between ADSL service providers
That's right - free, saving you £41. The ISP is Legend Internet and the offer is on their Go-Legend range which is £23.48 (inc VAT) per month.
Migration at present provides a smooth transition between service providers based upon you retaining the same ADSL product on the BT Wholesale side. Further migration options such as speed regrades are in the pilot stages now, and migrations between different products are due shortly.