Jeremy Warner: The excitement was not in new policies but working out how the trick had been done

Even assuming the economy grows, the estimates for tax revenue continue to look suspect

Stability, blah, resilience, blah, fairness to all, blah, blah, blah, yawn. But actually this was not as boring and unexciting a Budget as predicted. The excitement lay not in the Budget measures, which were mostly either pre-announced or leaked, as in trying to figure out how on earth the Chancellor had pulled off the conjuring trick of making the numbers stack up.

The answer lies in a combination of sleight of hand, sneaky little – and some not so little – tax rises dotted here and there around the economy, heavily laced with possibly quite unrealistic optimism about the outlook for the economy.

The other day, I suggested that the Chancellor wouldn't cut his growth forecasts at all given how tightly hemmed in he was on the public finances already.

In the event, he did trim, but only marginally by a quarter point for this year and next. Not that you would have guessed this from the Chancellor's gloom-laden comments in the Budget speech. These were every bit as downbeat as most outside forecasters, though with the mischief blamed firmed on the US housing crisis rather than any structural faults that might exist in the UK economy.

In fact, the forecasts are actually a good deal more optimistic about the outlook than the rhetoric. As it is, the tank is running on vapour, barely meeting the rules that are meant to keep the public finances healthy even if the Treasury's questionable assumptions about growth are met. If the economy fails to perform as anticipated, the Chancellor will bust them by a country mile.

Is the Chancellor's prognosis a credible one? The Treasury's record on economic forecasting is actually remarkable good. For the past 10 years, it has been consistently more right than most outside forecasters, and I struggle to recall a year in which it has been proved outright wrong.

It has also, at key moments of doubt, been consistently more optimistic. On every occasion before when the doomsters have said the economy is heading for hell in a handcart, its optimism has proved well founded.

Yet what makes things a bit different this time around is that there is nothing in the fiscal cannon left to throw at the expected downturn. In the economic contraction of 2001-03, the Government was able to counter the effect by turning on the spending taps. That's no longer an option. Alistair Darling has inherited both a poor fiscal position and a poor economic outlook, with the fruits of economic growth already spent.

While the Treasury has been spot on in its economic forecasting, it has been much worse at estimating tax revenues which, in recent years, have fallen short of expectations. Even assuming the economy grows by as much as the Chancellor thinks, his latest Budget estimates for tax revenue continue to look suspect.

Since the pre-Budget report in October. the Treasury has trimmed its estimate of tax receipts for next year a bit. As a proportion of national income, they are also expected to be marginally below what they were for this tax year. Income tax receipts are expected to grow by less than the rate of inflation.

Reflecting the drop-off in the housing market, stamp duty revenues too are expected to be a little bit lower. The Chancellor cannot, therefore, be accused of entirely ignoring the effects of the credit crunch. He's factored in some sort of a negative impact over and above that caused by lower economic growth.

Even so, the estimates continue to look on the high side, both for this year and next, as do the projections for the amount of tax raised by some of the Budget measures. Is it really credible that receipts from stamp duty will fall by only £800m in a year when housing market transactions are grinding to a halt? And is it at all likely that corporation tax receipts will increase in a year when the stock market is pointing to a severe squeeze in corporate earnings?

Many accountants are deeply sceptical about the numbers pencilled in for measures aimed at tax avoidance. Those are meant to add £660m to revenues this year, £590m next year, and a further £503m the year after, even though, in at least two cases, the Treasury is only closing off loopholes that haven't yet been used and as things stand therefore cost the Revenue nothing. More evidence, then, of the numbers being essentially made up to make the overall position look more acceptable.

The big picture in the Budget numbers is that the delay in implementing higher fuel duties, together with the costs of higher pensioner and child benefit, are to be paid for with higher taxes on alcohol, a rise in road duty and the reintroduction of car purchase tax on gas-guzzling vehicles.

The last of those measures, justified as an environmental tax but self evidently there mainly for the purpose of raising revenue, amounts to a splendidly ill thought out hammer blow to two of Britain's most successful car makers, Jaguar and Landrover.

In conjunction with Ken Livingstone's proposed £25 a day congestion zone charge, it will kill sales of those vehicles in the South-east of England, one of their main markets, stone dead, as well as sending out a hugely negative message to important export markets. Well intentioned greenery, no doubt, but you wouldn't find the Germans or Japanese being quite so cavalier with the prospects of their auto industries.

More disingenuously, the Government proposes to remove the duty differential on biofuels and "replace" it with a "renewable transport fuel obligation", never mind that the first of those measures saves the Government £550m a year while the second costs absolutely nothing since the obligation would eventually have to be brought in under EU rules anyway.

Still, the Budget has to rely on such tricks of the light to make the numbers look even vaguely plausible. Even on its own forecasts, the Government comes within a hair's breadth of breaching the sustainable investment rule, which dictates that public debt must remain at below 40 per cent of national income.

Perhaps the Chancellor will be lucky, and the credit crisis will go away, allowing the economy to enter recovery mode by the beginning of next year. Without that luck, we are back to the future, with ballooning deficits and steeply rising levels of tax.

There was little evidence in this Budget of the tax simplicity the Chancellor has set as one of his goals. The 270 pages of Budget notes sent out by Her Majesty's Revenue and Customs were said to be a record.

Another 12 reviews were piled on the 16 consultations on tax issues already under way. Even ignoring the credibility of the big numbers, that is not a tax environment conducive to successful business. The present challenge facing the public finances will look like a stroll in the park if the Government continues carelessly to kill off the golden goose with such abandon.