After months of speculation, we have the electoral deadlock which almost every opinion poll during the campaign had predicted, but with a division of seats between Labour and the Liberal Democrats which almost nobody would have foreseen.

It is also the outcome which is almost, but not quite, what electoral reformers have hoped for two decades or more. For, while there is no Conservative majority, there is only the most tenuous of anti-Conservative majorities - a prospective 'rainbow coalition' of Labour, Liberal Democrats, Plaid Cymru, the SNP, the Alliance Party, the SDLP and the Greens.  Even this might require a fantasy development to get to the magic figure of 326 - such as the newly-elected Zac Goldsmith suddenly defecting from the Tories to join Caroline Lucas as a Green.

Just how did we arrive at this outcome? And what does it tell us about the future of our party politics?

This was not quite the classic 'two-party squeeze' which some commentators have suggested. Rather, the story of this election is that both the Labour and the Lib Dem vote held up remarkably well in their respective strongholds, thereby blocking the Tory advance in two key battleground regions. 

Labour's electoral strategy ultimately came down to defending seats in its core areas of support. While Labour was never going to be facing electoral melt-down on the scale of the Tories in 1997, nobody had predicted that the Labour vote would have held up quite as well as it did, particularly in Scotland and in North West England - with the latter proving a crucial element in preventing a Conservative majority.

The lists of seats which the Conservatives failed to win in the North West is quite astonishing - among them Sefton Central, Wirral South, Blackpool South, and Bolton West. There are two obvious explanations for this pattern. First, many voters in the deindustrialised North West still have painful memories of the impact of Thatcherism. Second, the Conservatives are organisationally weak in the North West, having been wiped out on many local councils a decade or more ago. This lack of an organisation base was not going to be solved via multiple visits to the region from David Cameron.

The dramatic disappaearance of the 'Lib Dem surge' took everyone by surprise - although it would appear that the Lib Dem vote rose dramatically in some areas and fell sharply in others. Even within individual regions there were bewildering patterns. The Lib Dems unexpectedly lost in Liverpool Wavertree, but took Burnley from Labour. In Wales, they won the previously marginal seat of Ceredigion on a huge 10.6 per cent swing from Plaid, but lost the neighbouring, previously safe seat of Montgomeryshire on a huge 13.2 swing to the Conservatives. It was only in the South West, the region in which their support is most concentrated and entrenched, that the Lib Dem vote held up in any consistent way, again frustrating the Conservatives in their pursuit of key target seats.

All this suggests that tactical voting is likely to have played a major role in this election and that, for large numbers of voters outside the core areas of Conservative support, keeping the Tories out was their key priority. Lib-Lab may not have a majority of the seats by some margin, but between them they have won over 50 per cent of the vote. 

Tactical voting did not prevent the Conservatives winning in 1987 or 1992. But in 2010 it is likely to have played a significant role. The progressive anti-Tory majority coalition may or may not emerge from the negotiations taking place among the parties - but it would appear to remain quite deeply embedded within the electorate.