Squaring the circle
There are always three audiences for a Budget: voters, the City and the chancellor's own party.
The challenge for Alistair Darling this week is that for once, all three of them will be listening. Expect modest good news on the deficit; cautious language on the economy; and a "bold plan" to spur private investment in future growth.
We know what many in his party want: a Budget statement which actually helps Labour's standing in the polls. As Nick Robinson has pointed out, they never have in the past.
They also want him to make a link between government action in 2009, and the recovery in 2010. And to show that savings from the smaller than expected rise in unemployment can now be invested in Labour priorities, notably training and jobs.
We know what the City wants: a faster timetable for bringing down the deficit, an/or more clarity on how, exactly, it will be done.
Yes, investors know there is an election on. The bond markets are unlikely to be spooked by the chancellor leaving his deficit plan roughly where it is. But they will be very alert to backsliding.
He knows the City will not take kindly if he spends improvements in the underlying deficit rather than using them to cut overall borrowing. He did that in the pre-Budget report: arguably, he only got away with it because traders didn't think there was any chance that Labour would win.
And voters? As ever, voters are a not a uniform bunch. Nor are their polling answers consistent. We're told that voters will reward politicians for "telling it straight". That is the box that all three major would like to tick. But according to an Ipsos MORI poll last week, only 50% of people believe that public spending cuts will be needed to get the public finances in order.
Given that, perhaps it's no surprise to see from another poll this weekend that only 64% expect Alistair Darling to tell them the truth about Labour's plans. The figure for George Osborne was 62%.
Can the Chancellor square the circle? We find out on Wednesday. But here are my top predictions.
First, there will be no major change in the timetable for bringing down the deficit, or the balance between tax rises and spending cuts to achieve it. But I believe the chancellor will revise down the forecast for the structural deficit through to 2014-15.
That could raise an interesting quandary for the Conservatives. In their rhetoric they have seemed to focus on the current structural deficit - the part of the structural deficit that is not due to net public investment.
If the chancellor leaves his forecasts for net investment unchanged, then the structural current deficit could fall to less than 1% of GDP by 2014-15 in the Treasury's revised forecasts. The Tories will have to say how much further they would go.
Second, the improvement in the underlying picture will probably prompt a slight downward revision to the growth forecast for 2011. Other things equal, that would cause a rise in "cyclical" borrowing over the next few years. But that need not push up the headline borrowing numbers, if the structural deficit ha been revised down.
A slightly lower growth forecast for 2010 would give the chancellor another opportunity to talk about the "fragility of the recovery", which would otherwise look a bit strange next to a forecast for 3.5% growth in 2010.
But expect the Treasury forecast will stay well above the private sector consensus for 2011 - which is currently for growth of 2.1%. Officials think that is too gloomy, and they may be right. Remember that even 3.5% growth, after the two years that the UK economy has just had, would be much weaker than the recoveries we've seen in the past.
Third, the chancellor will not yield to business pressure to re-think the reduction in pension tax relief for high earners.
He knows it's going to be horrendously complicated to administer for companies with final salary pension schemes. He also knows there are other ways to prevent high earners from parking their income in pensions to avoid the new 50p rate - for example, by cutting the lifetime cap on the tax-free pensions pot, or the cap on the amount that can be contributed in a single year.
The problem is the Treasury doesn't think these steps would be as effective. And crucially, they don't think it would raise nearly enough cash.
Fourth, along with everyone else, I expect some modest new spending on jobs for young people, but no big giveaways which have "six weeks before an election" written all over them. Mr Darling ruled them out explicitly yesterday talking to Andrew Marr.
However, it is clear to me that there will be a major new initiative to stimulate private and public investment - along the lines of a national investment fund or bank.
As I've said before, this is something the Treasury have been thinking about for some time, to complement quantitative easing. It is also something that many city economists would welcome, assuming it doesn't try to micro-manage where or what the investments will be.
Such a scheme would give the chancellor something positive to say about the re-balancing of the UK economy, at a time when the other leg of that re-balancing strategy, a surge in exports, is looking very fragile indeed.
It is also something the Conservatives and Liberal Democrats would find it hard to oppose, given that they have talked about creating something similar themselves.
We've had a lot about taxing banks in the lead-up to the Budget. I'm sure that will play a role as well - which is, of course, why the Conservatives felt they had to get in first.
On the day, Darling will also be trying to make this a Budget for investment. In theory, all three audiences - voters, the City and his party - will be able to warm to the theme of raising UK investment. But only if they can see through the pages and pages of red ink.