Let’s get one thing out of the way first: the Labour Party exists to win elections.

We’re not a protest group or a glorified charity campaign, we do not exist to ‘raise issues’ or ‘start debates’. We exist to win a public mandate to change the country for the better.

This is important because it puts what happened in the General Election into context. A defeat on this scale is not just a bump in the road, it’s a crisis posing fundamental questions about our aims and objectives. This crisis requires a radical response.

That’s why the overwhelming focus of this leadership election should be picking a leader who can win in 2020. Not one who can ‘unite the party’, paper over the cracks and get big cheers at party conference. We need somebody who can beat the Tories and lead us back into power.

I’m also clear that the only way to beat the Tories is to reach out from our base and start winning Tory voters over to Labour. This may sound obvious, but it seems to have become a strangely unfashionable view in some Labour circles. I’m forever reading about how if just a few more Greens had voted for us, or if turnout was a little higher then Ed Miliband would even now be measuring the Downing Street curtains.

This is dangerous nonsense. Over 11 million people voted Conservative in the election, and if we make no attempt to win back those voters then Labour will never form a majority government again.

To win these people back, Labour will have to change. We will have to leave the comfort blanket of opposition and wrestle with the difficult issues that serious parties of Government must confront. This means fighting on unfamiliar turf, whether it’s defence spending or public service reform.

Some in Labour will say that this means adopting a ‘Tory agenda’, but if we allow ourselves to believe that wanting to defend our country or to make public services more efficient are Tory ideas then we might as well give up and go home. A party that seeks to win popular support and govern for the whole country must speak on issues that concern the whole country, not just those that excite its core supporters.

To do all of this will require a leader with bravery and vision. Someone who can move on from the past and think creatively about the challenges facing modern Britain. Someone who can ignore siren voices from all sides and stick to what’s right and what resonates strongly with the British public.

In my opinion the only leadership contender displaying these qualities is Liz Kendall and that’s why I’m backing her in the leadership contest.

Whether it’s reforming our public services to give people more control or carving out an ambitious new role for Britain in the world, Liz is the candidate who has been making the running and mapping out a platform from which Labour could take on the Tories. Liz would also offer Labour a fresh start. Free from endlessly debating the successes and failures of the Blair and Brown years, we could finally move the debate on to show what a modern Labour Party will do to improve the lives of millions.

Crucially, I believe Liz has the desire and determination to win in 2020. She understands that winning is not an afterthought in some great intellectual project, winning should be the aim. For too long pragmatic steeliness has been missing in our politics and we need to get the bit between our teeth again. Our desire to win elections should never be seen as a betrayal of our principles, but the truest expression of them.

Over the next five years I will see hundreds of constituents who are suffering because of the bedroom tax. The Labour Party could have helped these people, but they will continue to suffer because we couldn’t win an election. That should be a huge wake up call to every Labour MP and party member.

So I’m backing Liz for leader because I think she is brave and because I think she is right. But most of all I am backing Liz because I think she can win.