And local representation and accountability would be lost. Plus you resign yourself to permanent coalition governments, where back-room deals determine the direction of the country instead of elected representatives.
The north/south ideological split is an anomaly that may indicate that a change is needed, but not really as far as I can tell. The voters in the South - where there has always been more people and prosperity throughout the centuries - vote for the parties that will generate more overall wealth, which means that they will get richer. The voters in the north - where traditionally there's been more manual labour and a (perceived) tougher way of life - consider themselves the downtrodden masses and vote for parties that pledge to change all of that. Because they want to become the richer people, and they want the better way of life, despite what they may say about clinging onto their working class roots.
I don't think that will change any time soon, despite the increased nationalism of parties such as UKIP and the SNP, who have a certain level of support but - in contrasting fortunes - whilst the SNP managed to gather enough support in enough constituencies to win and displace the failed New Labour incumbents, UKIP really blew it by not managing to get enough people in enough constituencies translating votes into seats. That was most likely because there's a far stronger nationalist movement in Scotland than there is in the rest of the country. I appreciate it sounds unfair on UKIP supporters, but our system of local representation at national level means that that's the way the game is played. All parties know that, and they all prepare for elections in the way they feel is best for them. UKIP got it right in as far as generating a core vote goes, but they would have been better served had they not declared themselves a true challenger to the main parties and concentrated on fewer, winnable seats instead. If they had done so, we may well have fifteen or twenty UKIP MPs now instead of just the one. And their voice would be heard more in Westminster. As it is, they are a negligible force, and their voters - whose four million votes only returned a single MP - ought to blame the party tactics for the situation instead of the system.
On the matter of the system, it's worth remembering that it is skewed in favour of a Labour government after the boundary changes brought in by Tony Blair. The Lib Dems scuppered a proposed rebalancing when they were in coalition, and as a result an average Conservative MP needed to gain far more votes than an average Labour MP, or indeed an average SNP MP.
Basically, there are loads of historic and constitutional reasons why no system is truly fair, but we have the one we operate under, and the rules are clear. Stand in a constituency, get more votes than your opponents (even just a single vote) and you are elected. If your party gains the most votes, they are in power, either as a majority party or as the lead party in a coalition. There's little point fighting an election under known rules, losing, and then whining about it. Plan and execute better next time.