Imagine the Chancellor’s morning briefing today. NIESR — Britain’s oldest economics think tank — has just told the Treasury that the Iran war will knock at least £35bn off UK GDP, cut growth to 0.9% this year, and force the Bank of England to start hiking again as early as July. The damning bit isn’t the worst-case scenario. It’s that even the “benign” one — where the Middle East conflict resolves in days — leaves Rachel Reeves’ tax and spending plans labelled untenable. The fiscal headroom she had in March has, on NIESR’s own central case, already evaporated.
What NIESR Actually Said
NIESR — Britain’s oldest economics think tank — has just told the Treasury that the Iran war will knock at least £35bn off UK GDP , cut growth to 0.9% this year, and force the Bank of England to start hiking again as early as July.
The headline number is the £35bn drag on UK GDP from the war alone. NIESR cut its 2026 growth forecast from 1.4% to 0.9% and now expects the economy to barely move in 2027 at 1.0%. Inflation is forecast to race past 4% by early next year, which is why the think tank now expects the Bank of England to reverse course and hike rates as soon as the July meeting — the first hike since the cutting cycle began in mid-2024. That’s a complete pivot from the consensus going into Q2.
The worst-case scenario is uglier. If Brent crude hits $140 a barrel, NIESR’s modelling has the Bank’s Monetary Policy Committee hiking 150 basis points in total — undoing every single one of the six cuts delivered since July 2024. Inflation in that path runs above 5% through 2027. And the £23.6bn of fiscal headroom the Office for Budget Responsibility gave Reeves in March? Gone. All of it.
Why the “Benign” Scenario Still Crushes the Treasury
This is the part that should worry Westminster more than the worst case. NIESR’s central scenario is explicitly the optimistic one — Hormuz reopens, ceasefire holds, oil prices retrace. Even in that path, the report calls Reeves’ current tax and spending plans “untenable”. Translation: the Chancellor needs to either raise taxes, cut real-terms spending, or pretend her March numbers still hold. None of those options is electorally pleasant.
Stephen Millard, NIESR’s deputy director for macroeconomics, put it plainly: the “renewed period of instability and subdued growth” forces both Reeves and the Bank into tough choices simultaneously. The Treasury can’t defer to the Bank because monetary tightening is itself part of the headwind. The Bank can’t defer to fiscal because the energy shock is structural. They get to make their bad calls in parallel.
The Compounding Vulnerability Nobody’s Pricing
The longer-term concern in the NIESR report is structural and worth pausing on. UK growth has been weak since 2008. Inflation spiked harder here than in peer economies. Policy choices have been criticised on both sides. The result: when a shock hits — Iran in 2026, Ukraine in 2022, Covid in 2020 — Britain absorbs it worse than France, Germany or the US. There’s less buffer.
Vicky Pryce framed it bluntly: the UK entered this crisis with higher inflation and higher rates than peer economies, with less room to intervene. Jack Meaning at Barclays (LON: BARC) sees two opposing risks — embedded high inflation expectations vs. a weak underlying economy revealed once the shock passes — and worries the worst path is the Bank tightening hard enough to suppress inflation but tipping growth and unemployment over in the process. That’s not a forecast. It’s a description of the corner Threadneedle Street is being squeezed into.
What Reeves Is Probably About to Do
The political pressure is converging from three angles at once. Energy support: poorer households are about to feel a winter price shock the Treasury hasn’t pre-funded. Defence: post-Iran-war demands for quick increases to defence spending which NIESR politely calls “fanciful” given the headroom situation. And the structural reform debate — North Sea licences, carbon tax on imported energy, energy storage — all flagged in the report as relevant for the next shock, none of it cheap or quick.
Watch the autumn statement. Reeves has roughly six months to either re-find fiscal headroom (politically: tax rises, almost certainly), cut real spending (politically: cuts to anything popular), or accept higher gilt yields as the bond market re-prices UK risk (which compounds the problem because debt servicing eats more of the budget). For context on how that bond-market repricing already started: UK 10-year gilt yields hit 5% earlier this month, joint-highest since the 2008 crisis. The gilt market is already telling Reeves what NIESR has now formalised.
The political calculus is also worse than the fiscal one. A government that raised the personal allowance and pledged to protect day-to-day spending now faces a forced retrace. The defence-spending lobby will not accept “we’re skipping this round” gracefully. Pensioners on fixed incomes will not accept a winter-fuel cliff edge. Local authorities already running on emergency funding cannot absorb another real-terms cut without service collapse. Each constituency Reeves needs to lean on for the maths to balance has a megaphone, and most of them are now ready to use it.
There is one path that buys time without spending political capital — what the Office for Budget Responsibility calls “letting the automatic stabilisers work”. In plain English: accept higher borrowing in the short term, run a wider deficit to absorb the energy shock, and rely on the medium-term recovery to repair the headroom. The problem is that this is exactly what gilt markets are now sceptical of. A wider deficit at higher yields produces compounding debt service costs. NIESR’s report is essentially a warning that the cost of running deficits has risen sharply. The window to use that lever has narrowed.
The Bottom Line
The NIESR report is the moment the consequences of the Iran war stopped being a forecast and started being a fiscal fact for Reeves. £35bn off GDP. £23.6bn of headroom in the worst case — gone. A July rate hike that almost no one had on their card a month ago. The Chancellor’s next major decision is whether to acknowledge the new reality in October’s autumn statement or try to hold the March numbers and let the bond market do the acknowledging for her. One of those two paths leads to politically painful but credible fiscal repair. The other leads to a 2022-style gilt event with this government’s name on it. Watch which path she picks — it’s the most consequential call of her tenure.
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FAQ
How much of NIESR’s £35bn hit is recoverable if the Iran war ends quickly?
Even NIESR’s own “benign” scenario — fast Middle East resolution — keeps about half the £35bn baked in. The reason: oil-price futures, supply-chain repricing, and embedded inflation expectations don’t unwind overnight. The Bank still hikes 25bp in this path. Britain doesn’t get back to the March 2026 forecast even if the shooting stops tomorrow.
Why does the UK get hit harder than France, Germany or the US on the same shock?
Three structural reasons NIESR has flagged before. Energy import dependency is higher in the UK than US (no shale cushion) and higher than France (heavier nuclear). Inflation entered this shock from a higher base. And policy credibility is thinner after the 2022 Truss episode — bond markets price UK risk with a wider spread than peer sovereigns, so any new shock multiplies through gilt yields faster.
Is the Bank of England actually likely to hike in July?
It’s now the central case for NIESR, and pricing in the OIS curve has shifted that way over the past 10 days. The MPC’s August forecast round is when the new modelling lands formally, but the July meeting is the political pivot moment. A hold would tell markets the Bank is willing to let inflation run hot to protect growth — a serious credibility decision either way.
What does “untenable” mean in practice for Reeves’ tax plans?
It means the maths in the March budget no longer reconciles. Roughly £20-25bn of headroom assumed for the next four years has either evaporated (worst case) or been more than halved (central case). Reeves either raises taxes in October, cuts real-terms spending, or relaxes her fiscal rules — and the third option is what spooked gilt markets in 2022.
Could North Sea oil and gas relicensing actually help?
Not in the short term — NIESR is explicit that lifting restrictions on new exploration licences would not “alleviate” current pressures. The relevant timeline is years, not quarters. The report frames it as resilience for the NEXT shock, not a fix for this one. Energy storage and closing imported-energy carbon tax gaps are the higher-impact long-term moves.
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