For Labour activists, the fight at the coming election will be focused on the choice the British people will have to make between a Conservative or a Labour government. Yet, while the Tories are second to Labour in 308 of our seats, on the ground third parties are increasingly influencing the outcome of elections. Indeed, for 50 Labour MPs the Liberal Democrats are in second place, 42 face the SNP and 12, Plaid Cymru.

So, while the issue for the majority of voters is whether they want a government led by Michael Howard or a government led by Tony Blair, in nearly one in four of our seats we must ensure we are able to meet the challenges created by the presence of third parties.

As they do not offer the realistic prospect of forming an alternative government, these parties create a different challenge to our campaigning. This is a relatively recent phenomenon for British politics. In the 1950s, Britain exhibited all of the characteristics of a nation with an unchanging, two-party system as the electorate divided its support equally between Labour and the Conservatives. At that point in our history, third parties got no more than 10 per cent of the vote – in 1951 it was only three per cent. Yet, by the 1980s the situation had changed again as a quarter of all the electorate voted for third parties. Since then, this level of support for third parties in British politics has remained constant.

Accompanying this changing electoral landscape is the evidence that the relationship between the electorate and political parties is defined less by permanent support and more by a lack of interest in party politics altogether. Research conducted by Mori at the beginning of this year shows that around 35 per cent of the British public consider themselves to be Labour supporters, while 17 per cent see themselves as Conservatives, 18 per cent as Liberal Democrats and six per cent identify with other political parties. Yet, in contrast to 2001, when only six per cent of the public didn’t see themselves as having any political leaning at all, in 2005 that figure is now 15 per cent, and nine per cent of voters say they simply don’t know.

At a point when many people feel disengaged from party politics, therefore, the changing fortunes of third parties can be critical to the outcome at the ballot box. Indeed, turnout has been falling for a number of years. In these circumstances, those third parties that have little chance of forming a government can become effective vehicles for anti-political sentiments. These parties seek to portray every election not as a clash of competing ideals, but simply as a referendum on the government of the day. This allows them to sidestep neatly the critical issue of their own policy platforms and instead offer themselves as the alternative.

When I talk to activists in every constituency about these parties, they have their own story to tell. Just recently we have seen the Edinburgh Liberal Democrats campaigning against congestion charging despite their national support for the schemes. So, too, their health spokesperson, Patsy Calton, has campaigned for her local hospital in Cheadle to become a foundation hospital, despite having voted against this policy in parliament. The Scottish Nationalist MP for Perth campaigns for the retention of Scottish regiments within the British army at the same as her party seeks to break up not just the British army but the very idea of Britain.

In the new era of devolution to Wales and Scotland, the presence of a parliament and an assembly that deal with key issues such as health and education highlights the redundancy of the nationalist argument built on a perceived grudge and grievance towards the rest of the UK. And, regardless of their campaign rhetoric, the policy positions of third parties often bear little resemblance to their protestations of concern for social justice. The Liberal Democrats are a good example of this – their opposition to the minimum wage rises, proposals to abolish the New Deal, scrap the child tax credit and the pension’s credit show that far from being an alternative for disaffected Labour voters they would undermine many of Labour’s most important gains for working people.

So, too, the SNP oppose the child tax credit, the working families’ tax credit and the New Deal. Fringe parties like Respect and Ukip will no doubt continue to gain coverage and we know the BNP will seek to peddle their noxious messages. Yet, amid all of this, Labour’s duty to speak up for the hopes and needs of Britain’s working people endures. To get across that message in the months ahead is our challenge and our responsibility.

So what, then, is the best approach to take when dealing with third parties? As our campaign has highlighted, the challenge is to find ways to communicate our vision and our values in the changing electoral circumstances we face. This means reaching out to the electorate in ways that allow us to have the necessary shared discussions and deliberations about the issues of concern in our local communities. Whether through street surgeries, street stalls or coffee mornings, we need to engage the electorate in a meaningful debate about the issues that shape their hopes and aspirations.

There are many outstanding examples of campaigning Labour MPs who have been able to do just that and so cut through the anti-political rhetoric these third parties peddle. For example, as a party we can learn from the way in which, since 1997, MPs like Phil Woolas in Oldham East and Saddleworth and Lorna Fitzsimons in Rochdale have defeated the Liberal Democrats in highly marginal seats, and how David Stewart saw off the SNP in Inverness East, Nairn and Lochaber. These are politicians rooted in their communities, standing with them and speaking for them, week in and week out.

Indeed, these successes show that, while we rightly focus our national campaign on the contest between ourselves and the Conservatives, this places even more pressure on local candidates to get across the difference between our ambitions for the country and the empty politics of these third parties. We know such third parties offer little of substance in comparison to the aspirations that we have for Britain. Yet it is clear that the British public can tell the difference, too.

While third parties may exploit the comfort of opposition to shield the paucity of their policies, our recent by-election successes in Hodge Hill and Hartlepool show that, when we challenge them on their policy proposals, we can take on these parties and win. When local residents found out just what a vote for the Liberal Democrats would mean, they rejected them and recognised the difference Labour representation would make to their community.

So we must seek to hold to account all the opposition parties who challenge Labour – challenging them not on their opposition to us but on what they would do for the people they seek to serve. Our ability to do this only grows stronger as, in office, Labour delivers more of its agenda to transform Britain. In previous elections, we were able only to offer our vision of the future; now we can offer a stable economy, a track record of sustained investment and reform in our nation’s public services and a clear programme for the next term of parliament. Those who seek to offer only criticism or to be all things to all people cannot compete with the hope for the better future for all that a vote for Labour presents.