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The UK is about to report its fastest quarterly growth in over a year. The problem is that the same thing happens every Q1, and it always turns out to be wrong. This time, with the Iran war already battering the economy, the stakes for getting the data right are unusually high.
GDP figures due next week are expected to show the UK economy grew around 0.5% to 0.6% in the first quarter of 2026, a sharp rebound from the 0.1% expansion in Q4 2025 and the fastest quarterly growth since early 2025. February alone saw its biggest monthly rise in more than two years, driven by a surge in activity before the Iran war broke out.
On the surface, that looks encouraging. In practice, almost nobody thinks it reflects what is actually happening in the economy.
The Bank of England held rates at 3.75% in April, voting 8-1 to stay on hold, with its chief economist the sole dissenter calling for a hike. But the BOE has privately flagged concerns that the GDP data may be sending false signals, complicating the already difficult job of setting interest rates. In its most recent Monetary Policy Report it noted that Q1 growth of 0.5% would be higher than survey indicators suggest, and that it follows a pattern of unusually strong Q1 readings in recent years.
The Office for National Statistics, meanwhile, has admitted it found errors in the price indices it uses to calculate GDP, pausing publication of the affected data and warning of potential revisions going back to 2022. It is also under pressure from the statistics regulator to revisit its seasonal adjustment methodology after outside experts identified significant limitations. In response, the ONS said it would begin publishing non-seasonally adjusted GDP figures from next week to provide additional context, which is statistician-speak for admitting the main figures might be misleading.
Here is the pattern that should worry people. Between 2022 and 2025, UK GDP growth averaged 0.5% in Q1 and 0.3% in Q2, before slowing sharply to effectively zero in Q3 and Q4. Every year, a strong start gave way to a disappointing second half. Every year, the early optimism turned out to be premature. And every year, the ONS's seasonal adjustment failed to flag that the Q1 strength was being borrowed from later in the year rather than representing genuine economic acceleration.
The most plausible explanation is that spending patterns in the UK shifted permanently after the pandemic, with businesses and consumers front-loading activity into the first quarter in ways the ONS's models have not caught up with. Non-seasonally adjusted data supports this, showing Q1 moving from one of the weakest periods historically to one of the strongest since 2020. If that shift is real and the ONS is not accounting for it, then every rosy Q1 headline is essentially a statistical illusion that will be corrected, quietly, over the following two quarters.
The timing could hardly be worse. The Iran war broke out on February 28, meaning most of Q1 predates the full economic impact of the conflict. Inflation was already running at 3.3% in March and is expected to climb further as higher energy costs work through the economy. The BOE's own scenario analysis puts peak inflation anywhere between 3.5% and 6.2% depending on how long the energy shock lasts and how much it feeds into wages and prices. In the most severe scenario, rates could rise to 5.25% by 2027, a significant tightening that would hit mortgages, business investment, and consumer spending hard.
Against that backdrop, the reliability of the GDP data is not a technical quibble for statisticians. It is a policy-critical question. The BOE needs to know whether the economy entering this shock was genuinely strong or just appearing strong on a flawed seasonal basis, because the answer shapes how aggressively it needs to respond to inflation. If Q1 strength is borrowed from Q3 and Q4, then the economy was already softer than the data suggested before the war started, and the combination of an energy shock with an already-weakening demand picture is considerably more dangerous than it looks.
The ONS has had a difficult few years. Its labor market survey was described as virtually unusable. Its household wealth estimates required a £2.2 trillion revision. Its producer price indices contained errors going back to 2008. Each individual problem has a plausible technical explanation. But the accumulation of them, at a moment when policymakers are navigating one of the most complex economic environments since the 2022 energy crisis, is genuinely concerning.
Next Thursday's GDP release will get a lot of attention, but the more important date is May 12, when the ONS sets out its latest thinking on seasonal adjustment. If it acknowledges a structural problem and revises its methodology, the implications for how we read the past three years of UK economic data could be significant.
BP (BP) — Benefits from higher energy prices driven by the Iran war and general energy shock.
Shell (SHEL) — Benefits from higher energy prices driven by the Iran war and general energy shock.
ExxonMobil (XOM) — Benefits from higher energy prices driven by the Iran war and general energy shock.
Chevron (CVX) — Benefits from higher energy prices driven by the Iran war and general energy shock.
Oil & Gas Exploration & Production — Higher crude oil and natural gas prices directly increase revenues and profitability for producers.
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Crude Oil — Prices are expected to climb due to the Iran war and the resulting energy shock.
Natural Gas — Prices are expected to climb due to the Iran war and the resulting energy shock.
Lloyds Banking Group (LLOY) — While higher interest rates could boost net interest margins, this benefit may be offset by increased loan defaults and reduced lending demand in a weakening economy.
Barclays (BARC) — While higher interest rates could boost net interest margins, this benefit may be offset by increased loan defaults and reduced lending demand in a weakening economy.
NatWest Group (NWG) — While higher interest rates could boost net interest margins, this benefit may be offset by increased loan defaults and reduced lending demand in a weakening economy.
S&P Global (SPGI) — Potential for increased demand for alternative economic data and analysis due to ONS unreliability, but general economic slowdown could temper overall business.
Banking — Potential for higher net interest margins from rising rates is balanced by increased credit risk and reduced loan demand in a slowing economy.
Financial Data & Analytics — Increased demand for reliable economic insights due to ONS issues could be offset by broader economic contraction impacting client budgets.
International Consolidated Airlines Group (IAG) — Faces significantly higher operating costs due to rising energy prices (jet fuel) and reduced consumer demand from inflation and higher rates.
easyJet (EZJ) — Faces significantly higher operating costs due to rising energy prices (jet fuel) and reduced consumer demand from inflation and higher rates.
Tesco (TSCO) — Will experience reduced consumer spending and demand due to high inflation and increased household costs from rising interest rates.
Sainsbury's (SBRY) — Will experience reduced consumer spending and demand due to high inflation and increased household costs from rising interest rates.
Barratt Developments (BDEV) — Higher interest rates will significantly increase mortgage costs, dampening housing demand and investment.
Persimmon (PSN) — Higher interest rates will significantly increase mortgage costs, dampening housing demand and investment.
Rolls-Royce Holdings (RR) — Faces reduced business investment, potential supply chain disruptions from energy costs, and reduced consumer spending impacting various segments.
Unilever (ULVR) — Faces reduced consumer spending and demand due to high inflation and increased household costs from rising interest rates.
National Grid (NG.) — Faces higher input costs for energy and potential regulatory pressure on passing these costs fully to consumers.
Airlines — Highly susceptible to rising fuel costs and reduced discretionary consumer spending.
Retail (Consumer Discretionary & Staples) — Suffers from reduced consumer purchasing power due to inflation and higher interest rates.
Homebuilding — Directly impacted by higher mortgage rates, which reduce affordability and demand for new homes.
Manufacturing — Faces increased energy costs, potential supply chain disruptions, and reduced demand from both consumers and businesses.
Utilities — Faces higher input costs for energy generation and distribution, with limited ability to pass all costs to consumers.
UK — Faces significant economic headwinds from high inflation, rising interest rates, geopolitical conflict, and unreliable economic data, leading to a likely slowdown.
Medium-term BOE Monetary Policy Tightening — The Bank of England will likely be forced to raise interest rates more aggressively (potentially to 5.25% by 2027) to combat inflation fueled by energy costs, especially if underlying economic weakness is confirmed. This will further constrain economic activity. Confidence: High.
Short-term Increased Volatility in UK Equities — Uncertainty surrounding the true state of the UK economy, coupled with geopolitical tensions (Iran war) and persistent inflation, will lead to increased market volatility, particularly for sectors sensitive to consumer spending and interest rates. This will create a challenging environment for investors. Confidence: High.
Long-term Erosion of UK Economic Data Credibility — Repeated errors and methodological issues from the Office for National Statistics will diminish confidence in official UK economic statistics, potentially leading to misinformed policy decisions by the BOE and government, and poor investment decisions by businesses. This could hinder effective economic management. Confidence: High.
Medium-term Pressure on UK Consumer Spending — Higher inflation (driven by energy costs) and rising interest rates (impacting mortgages and other borrowing) will significantly reduce disposable income for UK households, leading to a contraction in consumer spending across various sectors. This will negatively impact retail and service industries. Confidence: High.
Short-term Boost for Energy Sector Profits — The Iran war and resulting "energy shock" will drive up crude oil and natural gas prices globally, leading to increased revenues and profits for major energy producers. This provides a counter-cyclical benefit to the energy sector amidst broader economic challenges. Confidence: High.
↑ Crude Oil Prices — Iran war and "energy shock" will drive prices higher due to supply concerns and increased demand for alternatives.
↑ UK CPI — Inflation already at 3.3% and expected to climb further, potentially to 6.2%, due to higher energy costs feeding through the economy.
↑ UK 10-Year Gilt Yield — The Bank of England's likely need to raise rates to combat inflation will increase government borrowing costs, pushing gilt yields higher.
↓ UK Consumer Confidence — Rising inflation, higher interest rates, and general economic uncertainty will depress consumer sentiment and spending intentions.
↓ UK GDP Growth (Actual) — The underlying economic weakness, masked by potentially misleading Q1 data, will become apparent in subsequent quarters, leading to lower actual growth rates.
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