I think it's fairly settled ground that politicians will happily experiment on areas where they're not going to gain many votes. For Thatcher, that was the north of England, Wales and Scotland. Blair was so intent on getting the votes of the south that he didn't push too far.
If you read up on the Poll Tax, it was actually the Scottish Tories that requested that the poll tax be implemented in Scotland a year ahead of England. The "Thatcher used Scotland as a sandbox" is a myth started by the Scottish nationalists. Like most of their whinges the facts are somewhat different.
Added to which I think there is a little bit of revisionism here. There are certainly areas of the north where very few people vote Tory but that certainly isn't true of the north as a whole IIRC the Tories actually beat Labour in terms of the popular vote and seats in 1983 in Yorkshire. The North West is probably very similar. It is not true to say that they didn't gain many votes there.
Edited by Northern Sol, 12 April 2014 - 10:57 PM.