Burnham's Budget must not be overshadowed by the OBR

The writer is the former chief of staff to Rachel Reeves and senior adviser to Keir Starmer

On the second floor of the Treasury's vast open-plan office on Horse Guards Parade is a memorial to Britain's fiscal history.

The front cover of every Budget document for the past four decades or so -- the "red book" -- is carefully framed and hung across two walls. A sea of red (and some questionable noughties graphic design from the New Labour premiership) hangs over the Treasury's strategy, planning and budget team, which is responsible for preparing the nation's annual Budget.

On October 28, a new cover will find its place on the Treasury's wall as John Healey delivers the first Budget of Andy Burnham's premiership. But what the new prime minister and chancellor will learn very quickly on the day is that it isn't the red book that matters, but the numbers in the "blue book", which is written half-a-mile down the road by the Office for Budget Responsibility.

The OBR's status in Britain's economic infrastructure has soared since its creation at the start of the last decade. It looms large as the independent auditor of the country's economy -- from its forecasts on growth, inflation and borrowing costs to picking apart the policy costings and tax measures of successive chancellors.

But it has become more than an economic institution. It is now (whether we like it or not) a major player in the political discourse. The decision of Liz Truss -- whose disastrous "mini" Budget in 2022 does not get a place on the Treasury's wall because it wasn't technically a Budget -- to bypass the institution propelled it to God-like status. The reforms introduced after the 2024 election further strengthened the OBR by preventing future governments from ever sidelining it.

I was in the room for the four fiscal events of the Starmer premiership. I would watch as commentators, journalists and others pored over the OBR's figures. Hundreds of hours would be spent by officials in the lead-up to a Budget on detailed policy measures and cabinet negotiations on public spending settlements. But on the day, there was less focus on what the chancellor said, and more on what the OBR concluded.

I know we were not alone in feeling politically impotent. When I served in opposition, I never read a single page of the red book. Instead, I spent Budget days photographing pages of the OBR document and pinging them to journalists on WhatsApp in a desperate effort to disrupt the then Conservative chancellor's message.

In its early days, the new Labour administration has shown competence in using the power of government to tell a story. An initial flurry of announcements has signalled priorities and given voters confidence that the new cabinet "gets it". This was followed by a successful Labour Party conference. But this month's Budget will put that storytelling ability under pressure -- Burnham won't be its sole author.

It would be a mistake for Number 10 to think it is a mere observer to the OBR's dominance. Ministers should not be buffeted by the official forecasts but seek to turn them to their advantage. If the Iran war has pushed up inflation projections, that is why the government has had to prioritise the cost of living. If growth is to be downgraded, then that's a mandate for further -- and more radical -- action. And if borrowing costs are rising, then the promise of fiscal discipline is about more than pleasing markets -- it is about delivering on the prime minister's "Makerfield Test" to protect family finances across the country by keeping mortgages and prices down.

The Budget will mark precisely one hundred days since the new government was formed. A symbolic milestone that will prove an early first test: how will it confront the hard economic trade-offs Britain faces? How will it fight to tell a compelling story over the noise and dominance of others?