Back to Labour when the Conservatives collapse, or a BNP analouge, but that's very unlikely.
The point I'm making, though, is that these voters went Tory in the first place because they liked Thatcherite economic policies. They'd already rejected both centre-Left economics as offered by the Alliance, and the hard-Left of Labour. I don't think there's anywhere else for these voters to go in the 1980s besides the Conservatives.