A misleading response!
This is the point of returning to BT -
I do know that they can be blocked on a "real" BT line.
Oh, I now see! BT can't block them but they know a device that can.
Then this device must be equally effective on a PN line, so there is still no point in returning to BT.
1999: Freeserve 48K Dial-Up => 2005: Wanadoo 1 Meg BB => 2007: Orange 2 Meg BB => 2008: Orange 8 Meg LLU => 2010: Orange 16 Meg LLU => 2011: Orange 19 Meg WBC