The only people that have an issue with the notion that the government should reflect the will of the people, David, are politicians, most notably those in government.
Tony Blair said, soon after being elected, that he saw the role of his back bench MPs as promoting the ideas and ideals of “his” government. He did not, he said, see their role as bringing their constituents’ wishes and concerns to Parliament. I use Blair as an example because he definitely said this, but there is no reason to believe that any other Prime Minister of any persuasion would think any differently.
There are large swathes of the UK where a particular party holds sway. The Tories dominate the shire counties and much of England south of the Wash, bar London. Labour MPs represent most constituencies in and around the big cities. Any of these areas can claim that they are being ruled undemocratically and in many respects they are. So long as party politics holds sway the party in power will concentrate its efforts on its core voters so a geographical bias will seem evident.
The SNP currently holds just 6 of the 59 Scottish seats. The LibDems have 11, the Tories one, with Labour holding the rest. It is very unlikely that huge numbers of Labour voters in the heavily populated areas in the South West of Scotland will defect to the SNP so in fact the SNP’s ability to influence the outcome of a General Election is extremely small.