This is exactly what BT were hoping you would do. The bundling of services is how they intentionally make it more painful for you to go elsewhere.
Totally agree, it's just sad that OFCOM can't/won't address the situation.
If necessary, when my BT 2 year contract expires next March I will migrate my BT Digital Voice LL to VOIP so automatically cancelling my BB (by current BT regime rules), will live with a possible/likely loss of BB for whatever period it takes to obtain FTTP BB only service from an alternative ISP of my choice at the time which certainly won't be BT.
Hopefully BT will perform a "clean" service termination at that time which won't inhibit any new ISP's ability to provide FTTP service within a short time period considering all the FTTP hardware will still be in place, with BT, who knows?