Between Now and April/May 2018
http://www.sinet.bt.com/sinet/sins/pdf/498v7p3.pdf
"It is prohibited to connect a device to a VDSL2 phone socket which has not passed BT's MCT (Modem Conformance Testing for SIN498). BT will be using OAM loopback to perform diagnostics on FTTC service and identify the CPE connected. Detection of unauthorised CPE may result in the following:
- Request for removal of unauthorised CPE
• Limitation or disconnection of Service
• Lack of support when troubleshooting faults
• Abortive visit charges or SFI Customer Misoperation charges when engineers find unauthorised equipment on site.
In addition, the usage of equipment which does not comply with the SIN 498 ANFP or interferes with other subscriber's service may result in the service being terminated."