Once a stop sell is in place you cannot order or migrate to other copper based services like ADSL or FTTC products. So what happens say if you ISP ceases trading (this has happened before with smaller ISPs), or you arent getting the speeds advertised so under your contract you can migrate away for free, when a stop sell is in place?
As mentioned above, if you have FTTP available to you and are on a stop sell exchange then you will be forced on to FTTP.
This applies to all of the following.... working line takeovers, start of stopped lines, migrations, CP transfers, addition of broadband to copper voice lines, bandwidth modify, or addition of lines and channels to existing installations.
There are pretty much no exceptions to this. Lack of local FTTP capacity being the only exception that I'm personally aware of.