Electoral stalemate looms amid decline of two-party dominance in Britain

With polls indicating that the May 7 UK general election is poised on a knife-edge, it is clear that the outcome could be decided, or at least strongly influenced, by events in Scotland. This is because that country, previously an electoral stronghold at Westminster of the Labour Party, appears to be undergoing a seismic shift in loyalty towards the Scottish National Party (SNP) following last year's landmark independence referendum.

This development represents a sea change in Scottish politics. And it could have profound implications for the longer-term future of the United Kingdom.

At the last UK election in 2010, Labour won 40 of Scotland's 59 parliamentary seats (with 40 per cent of the Scottish vote), with the Liberal Democrats securing 11 seats (with 19 per cent of the vote). However, following a surge in support for the SNP since last September's referendum, the party could boost the number of seats it has from the current six to 50 or more.

The importance of this should not be underestimated and has at least two fundamental implications. Firstly, it could threaten, once again, the territorial integrity of one of the world's longest standing political unions - between England, Scotland, Wales and Northern Ireland. Thus, although last year's Scottish referendum was supposed to cement the country in the United Kingdom for at least a generation, there is a significant and growing prospect of a second independence ballot in the next few years.

The prime reason for the transformation in the electoral outlook for the SNP lies in last year's referendum. That ballot, and the huge debate and interest it awakened in Scotland, means that the issue of how the country is governed (which is the party's strong-suit topic) has become the defining issue in the eyes of much of the Scottish electorate.

A second key impact of the SNP's rising fortunes in this week's Westminster election is a reduction of Labour's prospects of winning a majority in the House of Commons. Thus, though Labour could make significant gains in England on May 7 against the Conservatives and Liberal Democrats, the impact of these successes could be wiped out by losses to the SNP in Scotland.

The rise of the SNP, and indeed other "third parties", such as the UK Independence Party (UKIP) in England, may seem unrelated. However, there is a strong common thread that reflects the current flux in UK politics, in which a dominant two-party system is giving way to a more unpredictable, and uncertain, political landscape.

For much of the post-war period, UK politics has been dominated by the Conservatives and Labour. From 1945 to 1970, for instance, these two parties collectively averaged in excess of 90 per cent of the vote, and also the seats won, in the eight British general elections held in this period.

Yet, from 1974 to 2005, the average share of the vote won by the Conservatives and Labour fell significantly in the nine UK general elections. This has brought about a significant political change that is still unfolding.

It is the Liberal Democrats, to date, which have done most to break the hold of the two major parties on power. From 1974 to 2005, the average Liberal Democrat share of the vote in British general elections was just below 20 per cent.

However, several other parties have come to prominence too, including the SNP which already governs in the Edinburgh Parliament; UKIP, a party built around a policy of British withdrawal from the European Union; and the Greens, too. Reflecting this, five parties are currently each polling more than 5 per cent of the vote in England (six in Scotland) for the first time ever in modern UK political history.

The decline of the traditional two-party system makes it harder for any one organisation (not just Labour) to secure a majority government in general elections, making British politics more unpredictable. This is despite "first past the post" voting, which tends to provide the leading party with a significantly larger number of seats in the House of Commons than would be given by a more proportionate electoral system.

To be sure, coalitions and the sharing of power have long been a feature of UK local government and devolved parliaments and assemblies outside Westminster. However, this same dynamic appears now also to be permeating the heart of the British government itself.

Until 2010, when the current coalition government was formed between Liberal Democrats and the Conservatives, Labour and the Conservatives had won overall majority governments at every election since 1945, except for the brief interregnum between February and October 1974. Yet, as in 2010, it appears most likely that there will a second straight hung parliament.

This is, again, unprecedented in modern UK political history. And, it underlines the possibility that a second election may be required in coming months, as last happened in 1974.

Andrew Hammond is an associate at LSE Ideas at the London School of Economics, and a former special adviser in the UK government