My belief in a better politics is the reason why I support the alternative vote and will back the yes campaign in this coming referendum. The easy and politically expedient route would be to find an excuse to abandon my support now. But I won't.

I respect the views of my Labour colleagues who are for retaining first past the post. But I disagree with them. Why? Fundamentally, because AV offers an opportunity for political reform, ensuring the voice of the public is heard louder than it has been in the past. And given the standing of politics that is an opportunity we should take. It is a system that combines the direct representation of first-past-the-post with one that will make the votes of more people count.

We should be in no doubt. If Britain votes yes in May's referendum it will be a vote to challenge the status quo.

The very fact of having to gain the majority support of the voters will increase political accountability. AV will also force parties to admit where there is agreement between them, prising open our confrontational system so that similarities sometimes become as important as differences. It could be the beginning of a transformation in political debate.

For years the public have wanted to change the tone of politics. A vote yes is a vote to begin this change. Exaggerating disagreement in order to create false black-and-white choices under first-past-the-post has only added to a particular style of politics that turns off the electorate.

What about the objections to AV? It's not a proportional system, true. But no system is perfect. Its advantage is that it retains the essential link between one MP and one constituency. Breaking that link would be a mistake.

What about the objection that this is entirely irrelevant to the concerns of most voters? Yes, it is not at the top, or even near the top, of many people's lists of concerns. I cannot claim that voters in my constituency, or any other that I have visited, often raise the relative merits of AV versus first-past-the-post or any other system.

It is why I have always said that my top priority in a referendum held on the same day as the May elections would be those elections, since they provide the chance for a verdict on the Conservative-led government's vicious assault on many of the things we value. That remains so.

But how we make our politics more relevant to the concerns of the public is at the heart of the AV debate and should be the question underlying a whole programme of political reform.

This referendum should be just the first step to strengthen democracy by making it more representative of the people it serves. The disconnect between people and politicians that was so palpable in that angry year before the last election will not be bridged by a new voting system alone.

That is why I think that the next step should be reform of the House of Lords as well. I want to see a fully elected second chamber, as we and the Liberal Democrats called for in our manifestos – and I call on the government to bring forward those reforms as quickly as possible. David Cameron's use of the Lords in the past few months – packing it with peers to vote through his constitutional changes – shows again why that is so necessary.

Nick Clegg should make clear that he still supports a fully elected second house rather than another Conservative-inspired compromise. Certainly, I believe MPs – both Labour and Liberal Democrat – should be given the chance to vote for what was in their manifestos.

Can the AV referendum be won? If it is, it will be no thanks to this government. Clegg can't effectively campaign for it and Cameron won't. In the Downing Street rose garden they promised a new politics, but less than one year on Cameron chooses to stand with the status quo against political change, and Clegg cannot credibly stand for change because of his broken promises. This government can't deliver change in our politics when Cameron is unwilling and Clegg is unable.

And yet the public will get their say, and I will fight for a yes. I will join with those of all parties and none who want to see the public's voice heard more loudly in Westminster.

AV is no panacea for our political ills. Our political system needs bigger reform. But political change is sometimes about making small steps on the road. AV is a step worth taking. It's why I am urging a yes vote in the referendum.