Heatwaves are a familiar feature of UK summers, but the way they are recorded and understood has changed over time.
Today, a UK heatwave is defined as a period of at least three consecutive days where daily maximum temperatures meet or exceed the heatwave threshold for that location. Those thresholds vary by county, reflecting the fact that what is unusually hot in one part of the UK may be different elsewhere.
What counts as a heatwave?
The Met Office definition is deliberately location-based. A single hot day is not enough; the heat has to persist for at least three consecutive days. The thresholds were originally based on the 1981–2010 climate averaging period, but were updated ahead of summer 2022 to reflect the more recent 1991–2020 climate period. This update was made as the UK continued to see the influence of a warming climate, with eight counties seeing threshold changes and some moving from 27°C to 28°C, 26°C to 27°C, or 25°C to 26°C.
The records in this blog are compiled using the latest heatwave thresholds (1991–2020).
The longest UK heatwaves
Looking across the Met Office's UK heatwave dataset from 1900 to 2026, the longest recorded UK heatwave spell listed (where at least one station in the UK met or exceeded its heatwave threshold) is from 18 July to 25 August 1995, lasting 39 days. The second longest is the recent 2026 spell from 30 June to 5 August, lasting 37 days, followed by 26-day spells in 1947 and 1990.
Other notable long-running events include 1916, with a 24-day heatwave, and several 23-day spells, including 1976, 1983, 2013 and 2018. These figures show that prolonged heat is not new to the UK, but recent years continue to feature prominently in the records.
You can explore these records using the interactive graph below.
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Years with the most heatwaves
Some years stand out not just for the length of individual heatwaves, but for the number of separate heatwave spells. Analysis of the Met Office's UK heatwave data shows that 2025, 1992 and 1933 each recorded nine separate UK heatwave spells, where at least one station reached heatwave criteria. Next up were 1973, 1984, 2016 and 2022 with each recording eight.
This matters because a summer can be notable in different ways. Some years bring one long, persistent spell of heat, while others see repeated bursts, with temperatures easing before rising again above local thresholds.
Why 1976 remains significant
The summer of 1976 remains one of the most well-remembered in UK weather history. Heatwave spells were recorded in May, June, July and August, including a 23-day spell from 21 June to 13 July and a further 22-day spell from 6 to 27 August.
Its place in public memory is partly due to the persistence of the heat and dry weather. The records show that 1976 was not just a single hot spell, but a summer with repeated heatwave conditions over several months. That helps explain why it remains a benchmark against which many later summers are compared.
The 2022 milestone
While 1976 is remembered for duration, 2022 is remembered for intensity. On 19 July 2022, the UK recorded 40.3°C at Coningsby, Lincolnshire, the first time the UK had recorded a maximum temperature above 40°C. The Met Office described the event as a milestone in UK climate history, with the previous UK record exceeded by 1.6°C.
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There were several separate heatwave spells during 2022, including events in June, July, August and early September. These included a five-day spell from 16 to 20 July, covering the period of the 40.3°C record, as well as two 10-day spells in August and late August into early September.
A changing climate context
The changing heatwave thresholds underline an important point: heatwaves are assessed relative to the climate people are living in now. As the UK climate warms, the definition has needed to remain flexible enough to reflect current conditions. The update to the 1991–2020 climate averaging period was designed to keep heatwave thresholds representative of the “current” climate.
Historic summers such as 1976 remain central to the UK’s weather story, but recent records show that extreme heat is an increasingly important part of that story too. From long-duration events to the unprecedented 40.3°C in 2022, UK heatwaves continue to provide clear evidence of how exceptional heat can affect the country in different ways.
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