Hey Piers - how did you get on ?
We are wanting to do something similar at our property - we have recently received planning permission to convert our garage as an annex for extra living space. We are also with BT and would like to have a separate telephone line installed from the main house.
I contacted Openreach in the first instance and they told me to contact my provider (BT) to raise the request ?
Did you use your "Studio" address and register with another ISP ? I don't really want to be paying for another line until we have completed the build but would obviously like the lines installing ready for connection.
Your experience here is very welcome - thank you in advance 🙏🙏