Budget time, and the aftermath, is horrible for opposition staffers.

Endless meetings with politicians asking ‘what do we expect in the budget’ and evenings drafting multiple briefings just in case of each plausible scenario. A day locked in a stuffy shadow cabinet room on neo-lithic laptops, neck deep in crisps and biscuits poring over budget documents.

Days afterwards of impatient journalists demanding stories about it falling apart and endless talk of rabbits, shot foxes and gamechangers. This budget will have been no different.

The brains of the operation are the same as at my first budget in 2011. John Wrathmell, Ali Moussavi and Maighread McCloskey can skin and fillet a budget with their eyes closed. They are the brightest of all the bright people at Labour headquarters.

But the consequence of Labour's leadership hiatus is that for all the chatter about increases to the minimum wage a significant gamble George Osborne has taken has been missed.

I used to spend time gently suggesting to Shadow Cabinet colleagues that their quote on an obscure new tax break could wait while we made sure there was a single clear and coherent budget response from Labour.

This time, Harriet Harman and Chris Leslie have as usual done a hugely professional job. But as an unavoidable consequence of a leadership election each of the candidates has also responded. So Labour’s response will seem fuzzy to both media and electorate.

That presented an opportunity for George Osborne. Budgets always have fireworks - under which the Chancellor could have hoped to bury the scale of the bad news. He could have taken significantly tougher decisions than his targets required of him and thus left himself space to cope with the inevitable events that a Chancellor has to face.

Instead he made what could be a defining decision of this Parliament - and of his career.

He has still made some highly controversial and in my view unpleasant choices. But overall he has slowed the pace of deficit reduction to the point where even on his old fiscal mandate of a current surplus by 2017/8 he is only just meeting it. This is the mandate which until the planned vote in the autumn remains legally binding.

Indeed – he is only meeting it because of his stealth tax rises including on pensions’ contributions, energy bills and insurance premiums. Despite having disavowed the need for any tax rises pre-election.

Contrast this with June 2010 when he scrapped EMA, raised £12bn from VAT and in total announced £40bn in fiscal tightening by 2014/15. As a result when, in the face of events, he relaxed some of this he had bought himself the space to do so. And had left flexibility in his fiscal rules to get away with it.

This time whilst broadly sticking to his plan of an absolute surplus within this Parliament he has used up almost all of the wiggle room he had booked in at the March budget.

The new fiscal charter he intends to legislate for requires him to have an absolute surplus in 2019/20 - a specific date which is at least a change from any of his various fiscal plans in the last Parliament.

Yet following yesterday’s budget he is projected to only just achieve surplus in that year of £10 billion. That may feel like a lot but over four years there are many ways things could go wrong.

First, finding £17bn from departmental spending may sound less dramatic than the £41bn suggested in the March budget. But protecting defence, schools and DfiD spending – and adding £8bn to health spending – means the spending review and actually delivering it will be very tough. Not least as the services – social care, the police, sure start – most directly in the firing line have already borne the brunt over five years.

Furthermore the OBR has highlighted the revenue risk of his tax raising measures. Greece and China are competing to be the most worrying economic headwind. And with productivity and exports being revised down further how confident can the Chancellor be of even the current anaemic growth forecasts for the coming years?

If any or all of those things do go wrong then tax revenues will not deliver, welfare will overshoot and at some point George Osborne will be back in the commons asking people to vote for his fifth (yes, fifth) “long term” fiscal framework in two Parliaments. No doubt he will seek to make a virtue of it by claiming yet again to be laying a 'trap' for Labour.

Clearly, the reverse could also happen. Jonathan Portes has pointed out that before a recession economic forecasters often under-estimate the coming shortfall in growth – but in recovery they often under-estimate the bounce back.

If that latter happens then ‘Lucky General Osborne’ may find he can deliver his plans with room to spare.

I suspect that George Osborne thinks that that is likely. That would explain the Tory kitchen sink approach to their manifesto with more than £20bn in unaccounted for spending commitments. And it would explain him leaving so little room for error in meeting the surplus he is now legislating for.

A political journalist pointed out to me this week that George Osborne’s former adviser Rupert Harrison was always keen when setting such targets to leave a bit of flexibility for the inevitable events which are the curse of politicians.

In March I took a photo of our budget team in the Shadow Cabinet room knowing it would be my last there. I hoped it would also be George Osborne's last. I wonder if Rupert did the same knowing that whatever the result he was going to leave the Treasury.

And I wonder whether he’s taken the Chancellor’s ‘luck’ with him. If so then something - tax cuts, two per cent of GDP defence spending, the NHS or his fiscal targets - will have to give.

The job of the next Labour leader will be to make him pay for it. I can promise - having worked on the 2012 Omnishambles budget - that no matter how successful they are it won't be enough to win the next election on its own. And that their staff will still hate every minute of budget week.