Iran conflict poses 'very significant' risk to UK growth; FTSE 100 posts sharp sell-off

Executive summary

• The Office for Budget Responsibility (OBR) warns the Iran conflict "could have very significant impacts" on the global and UK economies. Key vulnerabilities include elevated energy prices, higher government borrowing costs and a fragile fiscal position.
• UK GDP per person remains roughly 30% below the pre-2008 trajectory, highlighting long-term productivity shortfalls that constrain fiscal resilience (GDP).
• Market moves: the FTSE 100 (FTSE) fell sharply, with intraday losses reaching as much as 3.7% to 10,417 points and a close down about 2.75% at 10,484. Major European indices also plunged: DAX -3.6%, CAC 40 -3.5%, FTSE MIB -3.9%.

Macroeconomic and fiscal snapshot

• Long-run output gap: Real GDP per person is approximately 30% below the path implied by pre-financial-crisis productivity growth — a structural drag on living standards and tax receipts.
• Headroom and borrowing: Chancellor headroom rose to £23.6bn from £21.7bn at the November update, but market turbulence tied to the Middle East conflict may quickly erode that cushion.
• Gilt market: The UK 10-year gilt yield has moved back above 4.5% from around 4.2% recently, reflecting repricing that reduces the likelihood of near-term policy rate cuts and raises long-term borrowing costs.
• Gilt issuance: Planned gilt issuance for the coming year is £252bn, around £5bn higher than prior expectations because of fewer Treasury bill (t-bill) issuances.

Energy, inflation and market channels

• Energy shock: Brent crude has risen to about $80 per barrel, roughly 18% above the OBR assumption used in the spring forecasts. Spot energy prices are up roughly 20% since the conflict began, implying an inflation impulse in the range of 0.5–1.0 percentage point if sustained.
• Inflation pass-through: A rule-of-thumb used by fiscal forecasters is that a persistent 10% rise in energy costs adds roughly 0.25–0.5 percentage point to headline inflation. Given current moves, the risk is for inflation momentum to stall plans for interest-rate reductions.

Labour market and growth outlook

• Unemployment: Forecasts show unemployment peaking near 5.3% this year, higher than previously expected and potentially amplifying demand-side weakness.
• Growth revisions: The OBR has trimmed near-term growth projections; GDP growth forecasts for the current year were downgraded, while later-year growth is expected to recover modestly under the central fiscal plan.

Tax receipts and public finances

• Record tax take: National accounts taxes are projected to rise from 34.5% of GDP in 2024–25 to a peak of 38.5% of GDP by 2030–31 — a historic high driven by frozen tax thresholds (higher personal tax take) and assumed asset-price growth (higher capital taxes).
• Fiscal vulnerability: Even with a planned path to reduce borrowing from 4.3% of GDP in 2025–26 to around 1.8% by 2029–30, debt dynamics remain sensitive to energy shocks and rising yields.

Housing and investment

• Housebuilding: Net additions to the UK housing stock are expected to fall from an early-2020s average of 260,000 units per year to a low of 220,000 in 2026–27, before rising to just over 305,000 by 2030–31 as planning reforms take effect. Lower near-term supply will weigh on construction-sector activity.

Market impacts and sector signals

• Equity markets: The FTSE 100 decline was broad-based — financials and basic materials were among the worst hit. IAG, the airline group, fell around 8% on the day, with miners and banks also materially weaker.
• Consumer pressures: Higher petrol, diesel and household energy bills will compress real incomes, with implications for hospitality, retail and discretionary sectors. Hospitality industry leaders point to tax distortions (standard 20% VAT on on-premise food) as a structural headwind versus grocery retailers.

Policy implications and risk scenarios

• Short-term: A sustained energy-price shock would likely delay Bank of England rate cuts, increase gilt yields and raise near-term borrowing costs for the government, reducing fiscal headroom.
• Medium-term: If energy prices revert, inflation would ease and the fiscal path could stabilise; if they persist, contingency measures (targeted household support or emergency fiscal spending) may be required.
• Recommended market-readiness actions for institutional investors and traders:
• Reassess duration exposure given higher gilt yields and increased issuance (GBP/duration hedges).
• Stress-test portfolios for a 10–20% rise in energy prices and a 50–75bp gilt repricing shock.
• Monitor fiscal-space indicators: headroom (£23.6bn), planned gilt issuance (£252bn) and tax-take trajectory (34.5% → 38.5% of GDP).

Quotable, citation-ready takeaways

• "UK GDP per person is roughly 30% below the pre-crisis trajectory, constraining fiscal resilience and long-term growth potential." (GDP)
• "Conflict-driven energy price rises — Brent near $80 — materially increase the risk that inflation remains elevated and that fiscal headroom will be eroded." (Brent crude)
• "Planned gilt issuance of £252bn and a 10-year yield back above 4.5% raise rollover and interest-rate sensitivity for the public finances." (gilts)

Conclusion

The spring fiscal update shows modest improvement in headline headroom and a higher long-term tax take, but simultaneous increases in energy prices, a repricing of gilt yields and an already weak productivity path leave the UK’s fiscal position more exposed. Traders and institutional investors should prepare for volatility across equities, energy and sovereign debt markets while monitoring key metrics: headroom (£23.6bn), gilt issuance (£252bn), tax take (peaking at 38.5% of GDP) and energy-price trajectories (Brent ≈ $80).