There has rarely been a Labour manifesto as important as this one.

The party still has a realistic chance of ending up the biggest party after the general election, but it remains pretty much tied with the Conservatives in the polls, Labour's MPs are fearful of a near wipe-out in Scotland, and with three weeks to go, voters are as lukewarm on Ed Miliband as they ever were. What Labour needs is a breakthrough and it is hoping the promises in the manifesto might provide it.

Its promises are only a small part of the picture though. In laying them out, Labour has sought to balance what radicalism they provide with a heavy dose of responsibility. The manifesto says a Labour government would freeze gas and electricity bills and rail fares; it would ban zero-hours contracts and raise the minimum wage to £8 an hour; and it would abolish the non-dom tax status. These are all good, solid ideas aimed at doing what Labour was established to do: make Britain a more equal society.

But the promises come with a bigger pledge designed to nail the doubts and concerns of many voters who look back at what happened the last time Labour was in charge of the economy. Miliband and his team have quite rightly been saying that the recession was caused largely by a global economic crash, but the manifesto also seeks to establish Labour as fiscally responsible. So much so that its front page is dominated by the clumsily-titled Budget Responsibility Lock - a guarantee that every policy is fully costed and will not require any additional borrowing.

None of that is likely to get hearts beating on the left of politics, but it also creates yet another problem for Labour in Scotland. Jim Murphy has been saying there will be no more cuts north of the border, but Ed Balls has admitted there will be and now the manifesto has explicitly committed the party to no more borrowing and a continuation of austerity in some form. Naturally, the SNP leader Nicola Sturgeon wasted no time in exploiting the difference and portraying her policies as an alternative to austerity, but that is not entirely convincing. The Institute for Fiscal Studies estimates there would be a gap of over £7bn if Scotland raised all its own revenue, and yet the SNP simply revives its accusations of fear-mongering. As an answer to questions over its economic plans, it is not good enough.

Labour believes that turning up the pressure on the nationalists in this area could win votes as part of a broader strategy, highlighted in the manifesto, to paint itself as the party of true economic responsibility. But the question is: will that be good enough to start seriously attracting votes in Scotland? On the face of it, the latest polls show that the answer is no, with TNS putting the SNP at 52 per cent, which is six points up on last month.

However, beneath that headline figure, the picture is more complex. In particular, there is still a large swathe of the electorate that is still making up their minds - some 29 per cent, rising to as much as 39 per cent in the important battleground of Glasgow. Jim Murphy believes, or is hopeful, that many of those will switch to Labour as election day looms (they may also be "shy" Labour voters in the way that many people were "shy Nos" during the referendum). The effect of tactical voting diluting the SNP surge should also not be underestimated, but hopes of avoiding a wipeout still depend on the Labour campaign taking off in a big way, and there is still no serious sign of that.

Will the manifesto change that? To the extent that it tackles concerns that Labour is not to be trusted with the economy, it might do, but the manifesto can never tackle another serious weakness in the campaign: Mr Miliband himself. So far, the Labour leader has had a reasonably good campaign, but Labour's manifesto and its campaign could do with more of the eye-catching, inventive ideas, such as the end of the non-dom status, that could get voters interested. We now know all about Labour's Budget Responsiblity Lock; it is just a pity that the party has done more to unlock its old progressive instincts and told us more about what it would do to make Britain a better place.