A game-changing Budget?
George Osborne may or may not deliver a memorable Budget speech tomorrow - but in two key respects his first Budget has already broken the mould. Because we now have a coalition government, the key decisions had to be taken with a Liberal Democrat in the room. Because we now have the Office for Budget Responsibility, the economic thinking behind those decisions is going to be there for all to see.
By all accounts, coalition government has introduced a degree of discipline to the entire process. "It's the end of government by sofa", was the way one senior official put it to me, with a sigh of relief, when the Budget negotiations were already well-advanced. The need to keep Danny Alexander, the Liberal Democrat Chief Secretary, in the loop meant much less scope for last-minute stitch-ups, or 3am additions the morning of the speech.
The OBR had to be in the loop as well, because it needed to decide how Mr Osborne's policies would affect the forecasts it made last week. If the chancellor announces big new tax increases on Tuesday, the change in the OBR's economic forecasts may not steal the biggest headlines. But they will make for interesting reading all the same.
Looking again through this new body's pre-Budget forecasts, published last week, I am struck by the amount of detail. For the first time, in an official forecast, we have year-by-year forecasts for house price inflation through to 2014-15 - and unemployment. And financial sector profits. We also know exactly what it is assuming will happen to short and long-term interest rates over time.
This is good news for journalists - and a great step forward for transparency. But it also means that we will find out some of the most interesting news in the Budget, after Mr Osborne has sat down. Because only then will we see exactly what the OBR thinks the impact of his tax increase and spending cuts will be on the broader economy.
Of course, the forecasts for growth and unemployment will come laden with political implications - Labour is already flagging up the fact that growth will be revised down next year and probably after that as well. Unemployment may look higher in the short-term as well.
Mr Osborne's people say it's not a fair comparison, because last week's forecasts assumed away any negative bond market reaction to cutting borrowing on Labour's slower pace. The reason is that they used current market interest rate expectations to derive those forecasts for future borrowing rates, which now obviously build in an expectation of Tory-Lib Dem cuts - not Labour ones.
There is something to this, but only Sir Alan Budd knows how important this distortion really is.
You can find many people in the markets who agree with the Conservatives' long-running assertion that Britain would have struggled to find a market for its debt if the old government had stuck to its path for deficit cuts. But you can also find people who think the fear of a run on gilts is overdone.
Whichever view you take, it is just that - a subjective view. Precisely because the road was not taken, we will never know where it would have led.
Only Sir Alan and the other members of the OBR know whether they think Mr Osborne's actions, on their own, will be a net positive for economic growth next year or a net negative, in the short run. My guess - and hope - is the explanation accompanying tomorrow's new forecasts will make it fairly clear.
So much for the (politically interesting) fine print. What about the headlines?
On borrowing, of course everyone will be looking for the chancellor's target for the structural budget deficit in 2014-15, and especially the part of the structural deficit that is not due to spending money on public investment, the so-called structural current deficit.
As I outlined last Tuesday, the latest OBR forecasts have probably left Mr Osborne looking for at least £25bn in further tax rises or spending cuts if he wants to take that structural current deficit to zero over the Parliament. That's a bare minimum. The chances are that the figure will be well over £30bn.
If he wants to stick to a 4:1 ratio of spending cuts to tax increases, he could simply accept Labour's planned tax rises and plan to achieve all of that additional £30bn-plus tightening through spending cuts.
But, we already know he wants to avoid some of Labour's National Insurance increase, and raise personal income tax allowances by £1000. (Kudos, incidentally, to my colleague Hugh Pym, who gave me this piece of Mr Osborne's Budget plans when the ink was barely dry on the coalition agreement, back in early May).
Higher taxes on air travel, and reforming capital gains, can and will help him square the circle. The big question is whether he will need to look elsewhere.
Last week I suggested that the government had many good reasons to avoid a big rise in VAT - even (or especially) one that is pre-announced for next year. After all, that is exactly what Japan did, some seven years after their financial crisis started, with disastrous consequences.
For that reason, I had thought it more likely Mr Osborne announce only a conditional rise in VAT - which would kick in only if certain deficit targets were not met - or that we would see Mr Osborne announce plans to devise and implement a comprehensive carbon tax instead of a rise in VAT.
But, clearly, this is not the accepted view of most - let's face it, any - leading commentators. Either this government has pulled off the most elaborate exercise in expectations management in living memory, or the chancellor has decided he does have to raise VAT in this Budget after all.
However even if VAT does go up, we know for sure that the bulk of the work is going to be done through spending cuts, about which we will surely hear only a few choice nuggets in the Budget. Anything else would be pre-judging the results of all that public consultation over the Spending Review, which is due to reach its conclusions by the second half of October.
The heated talk in Westminster is that this will be a "game-changer" Budget - one that sets the contours for government spending and taxation for many years to come. That may well be true. But it feels like we've had a lot of game-changing statements from British chancellors in the past few years.
Arguably, it was the pre-Budget report for 2008, with its devastating revisions to the scale of UK public borrowing long into the future, which truly set us on the road to this point.
It's worth remembering that around two-thirds of the "tough choices" being announced by the chancellor in this Budget have already been sketched out by his predecessor, in the past few Budgets and pre-Budget reports.
Yes, Mr Osborne's first Budget speech will be another step in the road toward decisions and policies which will indeed change our government - and our economy - for years to come. And yes, he will be giving us some important signposts for what is to come. But we're not there yet, and nor is Mr Osborne.
As he - and Alistair Darling - know well, the really tough decisions don't come in setting the headline spending totals, but in deciding how, exactly, they are going to be met. On that larger task, this government has moved further than its predecessor, with its £6bn spending cuts and its lists of cancelled projects. But when Mr Osborne sits down on Tuesday he will still have barely begun.