Sitting in the audience at the Progress manifesto conference last weekend was like seeing a potted history of Labour in government since 1997. Speakers included former ministers, a former special adviser, Labour members of parliament, a cabinet minister, Labour PPC and dozens of Labour activists and Progress members.

All of us were there to contribute to what has already been, by most standards, a lengthy and generally inclusive process of producing Labour’s manifesto for the next general election. Almost two years ago I attended a session with Labour’s manifesto coordinator Ed Miliband and members of the Labour Staff Network to share ideas for the manifesto, one of hundreds of such events of which the Progress conference was the latest.

So well done Ed, for taking on the first challenge for the manifesto – making sure it reflects the views of the entire party. The second task for the manifesto is even trickier – it has to give people a reason to vote Labour at the next election.

The manifesto of any political party is never going to top the bestseller lists, but it presents a unique opportunity for a party to set out its vision for the next five years and, if elected, gives the government a popular mandate for its policies. Without it, implementing controversial policies can be challenging, even for a party with a healthy majority in parliament. Labour’s manifesto in 2001 had nothing to say about foundation trusts – these and many of the government’s other public service reforms were always going to be controversial, but had the manifesto had more to say on these issues then the government could have pointed to a popular mandate for its reforms.

Modern political manifestos of all colours frequently seem to jostle with one another for which can say the least. The manifesto has become a peripheral document – largely ignored by the public and catching only the fleeting attention of the media. And for a party in government the temptation to play it safe and trumpet past achievements can be great. Labour’s campaign in 2005, for instance, was notable for its emphasis on past achievements, including the government’s handling of the economy.

We should be rightly proud of our achievements in government, but we cannot campaign on them alone. The world has changed since 2005 – Labour faces an electorate that wants to know what each party is going to do to improve their lives and an opposition that has overhauled its policies and its presentation.

Put simply, we can’t win by playing it safe. A monochrome manifesto won’t cut it. I don’t underestimate the scale of the challenge Labour faces at the next election – of course the Conservatives want to paint the next election as a choice between ‘change’ and ‘more of the same’. If we let them, we can’t win. The manifesto provides a unique opportunity for Labour to demonstrate that we understand the changes we need – to our economy, our politics and our society – and that we can provide them.

If we are going to produce a manifesto that gives people a reason to vote Labour then any idea worthy of inclusion should pass two simple tests – the Wednesday test and the Friday test. If the election is held on a Thursday, then any manifesto policy has to be sellable on the doorsteps on Wednesday – it has to be bold and memorable. But it must also be deliverable on Friday – it has to be properly thought through and costed.

A friend of mine who is a Conservative activist said to me the other day that Labour’s manifesto doesn’t need to pass the Friday test, since we won’t be in government after the election. I profoundly disagree. But if Labour is to demonstrate that it has a serious agenda for the next five years then its manifesto needs need to be credible – that means having policies that are costed.

With probably a little over two months until the election starting gun is fired, there is still all to play for. The next election won’t be won or lost on the strength of our manifesto, but it can provide the platform for Labour to demonstrate we can still be the change makers in British politics. Tony Blair once said Labour was at its best when it was boldest – let’s make that the theme of our manifesto.

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