surely a DPA breach
If you have previously made your opt-out preference clear, then any internal change by local authority is irrelevant. They have the ability to transfer those recorded preferences from the old copy of the register to the new one, and that's what they should do.
If it's OK for them to do this this year, and make everyone re-specify their opt-out preference, is it going to be OK for them to make a similar change next year too?
If it's OK for a local authority to pull this stunt, is it OK for any data controller to do it too?