A community fibre project does not necessarily go anywhere near BT infrastructure.
The incoming connections will be sourced from whichever provider offers the most cost-effective solution, which may or may not use any BT infrastructure.
Depending on the type of deployment, the end-user connections may use:
- the copper from the BT cabinet, siting their own cabinet nearby (sub-loop unbundling to provide FTTC)
- BT ducts and poles only (physical infrastructure access)
- their own trenches and other civil engineering (or the use of assets leased from an organisation other than BT)
In reality, it's a case of the most cost-effective solution for each link.