I think the north south divide is only useful in terms of England. Scotland which has an economic output comparable to the 'south' has it's own internal divides.
Indeed. Scotland has the Scottish National Party, which mucks up comparisons between Scottish and English politics.
However to answer your question, I think the Tories are definitely much weaker in the "North" than they used to be. In Scotland for example, they used to have respectable share of the vote and seats. I think they only have one seat in the whole of Scotland now, and they form government!