Gilt sales this year are forecast to be £220bn - way above all market forecasts.
There will be a big gulp from investors.
Why is the Treasury's borrowing need so much greater than was expected?
Well, the cost of bailing out the banking system appears to have been greater than expected.
I'm not surprised that sterling is now falling.
Questions will also be asked again about whether the UK will retain its AAA credit rating. If that were lost, the cost of selling all this debt would rise.
And then there will be the emotional reaction of bankers to the news that their take-home pay is being cut significantly by the new 50% top rate of tax and a reduction in relief on pension contributions for high earners.
There'll be gloom in the City tonight.
UPDATE, 14:10: Guess which single policy measure announced in the Budget represents the biggest single drain on resources and the largest individual stimulus measure in the current difficult year?
Not help for low earners.
Not support for pensioners.
Not support for the young unemployed.
Actually, it's the increase to 40% in tax relief to businesses on capital spending, for one year only - which is forecast to cost £1.64bn.
In fact, support for business in the current year looks pretty substantial. The total cost of deferring business rate payments, the car scrappage scheme, a fund for investing in young start-up companies, and various other smaller initiatives is over £3.3bn.
So although business leaders will hate the new top rate of tax, their chagrin may be tempered by the succour their companies are being offered.
UPDATE, 17:35: I haven't written much about one element of what I said early this morning I would be keeping an eye on, namely the credibility of the chancellor's growth forecasts.
That's because Stephanie Flanders has been highlighting all the reasons why the Treasury's expectations of a pretty sharp economic recovery may be far too optimistic.
If growth turns out over months and years to be even a bit lower than the Treasury expects - and many economists expect growth to be significantly lower - that would imply that the government will be borrowing even more, the public-sector debt will approach 100% of national income and it'll take even longer than seven years for debt as a proportion of GDP to start falling again.
Yuk and yikes.