Watching Philip Hammond deliver his third budget, it was hard to avoid thinking that an election must be in the offing. Chancellors normally show their mean streak when parliaments are young and squirrel away any available cash so that they can give money away as polling day approaches.

Not this time, though. The chancellor was in the position of knowing that public borrowing this year is on course to be £12bn lower than was predicted in the spring – an extremely happy outcome given the economy’s mediocre performance.

Less than 18 months into the current parliament, Hammond could have saved his windfall and met his stated aim of balancing the budget by the middle of the next decade. Instead he decided to blow the lot – in higher spending and an unexpected income tax cut.

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The independent Office for Budget Responsibility (OBR) says the UK will still be in the red by 2023-24, although in reality a great deal depends on the sort of Brexit deal the government secures. Hammond expressed cheerful optimism about the double deal bonus he would get in the event that negotiations end successfully: the end of the uncertainty that has led firms to mothball investment plans will lead to stronger growth, and there will be no need to keep money aside for a no-deal outcome.

Even so, the chancellor had to accept that he might be back with another package of measures in the spring if talks between London and Brussels break down over the coming months. In those circumstances, there will be pressure for a significant loosening of fiscal policy and all talk of balancing the budget by the middle of the next decade will go out of the window.

The budget was unashamedly political both in its tone and its content. Hammond used every opportunity to take a swing at Jeremy Corbyn and John McDonnell on the Labour benches and took delight in announcing that there would be no more PFI projects on his watch.

There could be only three possible explanations for Hammond’s approach. One is that he has overnight morphed into a born-again Keynesian and has decided that a bit more growth is the way to lick the public finances back into shape. That seems unlikely.

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A second is that the government secretly believes it is heading for a no-deal Brexit, so is giving the economy some padding before expected disruption during 2019. But if that were the case, Hammond would be keeping every bit of ammunition in reserve, not spending it now, so that does not seem all that probable either.

That leaves the third and final explanation, which is that the real architect of this budget was Theresa May – not Hammond. As the chancellor rather ruefully said, it was the prime minister who announced an extra £84bn over five years for the NHS back in the summer, thus depriving him of a rabbit to pull out of the hat.

What’s more, May then went further in her party conference speech and said that the public needed to know that the age of austerity was over. Those interventions left Hammond with very little wriggle room but in truth are a sign of the government’s weakness. While Hammond boasted of the lowest unemployment since the 1970s, there was no mention of the worrying trends of recent years: flat-lining productivity, persistently weak investment, wages lower than they were a decade ago once inflation is taken into account.

May has come to the conclusion that the public is sick of austerity, so Hammond’s unenviable task was to make it look as though everything bad that has happened over the past eight years was Labour’s fault.

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The chancellor made the best of a bad job and even managed a bit of push back to show that the Treasury was still committed to fiscal rectitude. Extra money for universal credit, repairing potholes and for schools can’t disguise the fact that austerity hasn’t come to an end. The Resolution Foundation thinktank calculates that the budgets of non-protected departments will be 3% lower in per capita terms in 2023 than in 2019. The freeze in working-age benefits for next year is still going ahead, saving £1.5bn.

The OBR’s bottom line is that the budget means an extra £1.1bn this year, £10.9bn next year and £23.2bn by 2023-24. No chancellor – not even George Osborne – in the run-up to the 2015 election – has been so generous since the fiscal watchdog was set up in 2010.

Hammond’s attempts to show that his generosity was grounded in fiscal discipline cuts little ice with the OBR. It noted sniffily that the budget had the “familiar Augustinian pattern of a near-term giveaway followed by a longer-term takeway”. St Augustine, it might be remembered, was famous for saying: “Lord make me chaste, but not yet.”