Proudly independent or not, the Office for Budget Responsibility (OBR) has become George Osborne's best friend in politics.

It never lets him down.

The office's forecasts allow the Chancellor to play tricks with time, to treat possibilities as certainties. Forget past and present, he seems to say, attend to the future, when all will be well. So he ticks off the promised years ahead, each one better than the last, as though his victory over the dragons of debt and deficit has already been won.

This would be fair enough if the OBR's record in the soothsaying business was a little better than it is. That simply isn't the case. The office has erred on the side of optimism repeatedly since the Coalition came to power. Inflation, wage growth, productivity, debt and deficit: the OBR's history is not a happy one.

In 2010, to take the obvious example, the office declared that the Coalition's tax and spending plans would be enough to balance the books by 2014-15. So here we are: Mr Osborne has borrowed £90.2 billion thus far this year while debt is 80.4 per cent of GDP. As things stand, the UK owes £1,485 trillion.

Over five years, the Chancellor has made plenty of promises of his own. In June 2010 he awarded himself a "formal mandate" to ensure that "the structural current deficit should be in balance in the final year of the five-year forecast period, which is 2015-16 in this Budget". Yesterday, Mr Osborne instead picked 2018-19 as the blessed year when Britain will at last move into surplus. And that, it seems, is a promise.

But what else would a Chancellor say just seven weeks from a general election? That he has been wrong consistently, that signs of improvement do not count as a cure, that the precedents for his predictions are less than encouraging? That was never likely. It is worth remembering, nevertheless, that everything forecast yesterday for the end of the next parliament was supposed to have happened by now. The fact does not inspire confidence.

A similar vagueness afflicted the Chancellor when it came to the spending cuts he hopes to make by 2017-18. He has £30bn in mind, £13bn of it from government departments, £12bn from welfare, and £5bn from action on tax evasion and avoidance. But which cuts, where, how? The impression left was that Mr Osborne had picked numbers to suit his endlessly-adjusted targets.

Politically, this was not "the long-term plan". The 2010 idea was for a short and sharp five years of deep austerity that would allow the Chancellor to hand out treats ahead of May's election. In reality, and despite all the talk of windfalls, he has little enough to offer: pensioners and savers will enjoy their rewards in due course. The rest of us will have to hope that Mr Osborne's new, improved standard-of-living measure is more credible than it sounds.

"Out of the red and into the black," he trumpeted semi-poetically. "Britain is back, paying its way in the world today." It was a nice bit of doggerel. It also happened to be untrue. As Ed Miliband observed when his chance came, the gaping holes in Mr Osborne's pretty canvas are caused by non-existent productivity growth and a shortfall, irrespective of the job numbers, in tax revenues.

Nevertheless, the Chancellor identified several windfalls for which he duly claimed credit. Then he congratulated himself for refusing to be "irresponsible" with his good fortune. He means to sell £13bn of mortgage assets remaining from Northern Rock and Bradford & Bingley and realise £9bn from Lloyds shares. With lower unemployment implying "less welfare", and interest charges falling thanks to the lucky break of low inflation, he could ease austerity. Instead, Mr Osborne will "pay down the national debt".

In plain language, he needs his windfalls to meet his latest targets. He needs these considerable sums just to get the UK even close to a £7bn surplus - if nothing else goes wrong - by 2019-20. Along the way, if re-elected, Mr Osborne intends to hack away at the state and the welfare guarantees the state once offered to its people.

He has no other strategy, it appears, for reaching that £7bn, even with his windfalls. In essence, the £7bn will be withheld from public services just so Mr Osborne can claim a belated triumph. Still, treat the huge sum as a small mercy: last autumn, the Chancellor had a £23 b surplus in mind

Meanwhile, forecast UK growth will settle - though the Chancellor didn't admit it - at just below its long-term trend rate of 2.5 per cent a year. That dry jargon best expresses where the UK truly is as a country: improving slightly, but with the highest hope of returning to being no better off than our 30-year statistical average. Growth remains weak, yet this is the plan, if plan is the word, to which Mr Osborne is determined to stick.

Of practical Budget measures there were few enough among the statistics. Plainly, the cut in Petroleum Tax Revenue (50 per cent to 35 per cent) and the reduction in the supplementary charge (30 per cent to 20 per cent) are crucial amends from a Chancellor who raided North Sea revenues not so long ago. Whether they lead to a 15 per cent increase in production - another OBR guesstimate - remains to be seen.

That aside, the Chancellor who promised no pre-election "gimmicks" was not above dangling a few. A "help-to-buy ISA" to revive a housing boom? The unlocking of pension annuities for all who have them? A promise to raise the higher tax rate threshold at last? If none of those appeal, let friend George knock a penny off the price of your pint.

It says something about the real state of the British economy that these gestures were as much as the Chancellor could afford - actually afford - in terms of electoral politics. The country might be recovering from the bankers' crash, but it remains the slowest recovery in the UK's history. It is too little, and comes far too late, to make much difference to the Conservatives' general election hopes.

And that was never a part of Mr Osborne's long-term plan.