The UK could see its first-ever national heatwave emergency this weekend amid fears of record-breaking temperatures, with officials braced to take unprecedented action if it is deemed necessary.

Forecasters at the Met Office are predicting that the mercury will exceed 35C on Sunday – but have warned that some meteorological models are producing maximum temperatures in excess of 40C.

Ministers held a Cobra meeting yesterday as a weather warning was issued and the Cabinet Office is coordinating a cross-government response between a host of departments and agencies.

According to the official Heatwave Plan for England, the decision on whether to declare a state of emergency would be taken following a cross-government assessment of weather conditions, coordinated by the Cabinet Office.

Southern parts of the country have already been placed on the second-highest level of alert this week by the UK Health Security Agency (UKHSA), a measure which requires health and social services to take action to protect vulnerable people.

However, a UKHSA official was reported as saying that “if it gets above 40C then it is likely to be a level 4 heatwave for the first time”, meaning a state of national emergency will be declared, adding: “I don’t see how it couldn’t be in those temperatures.”

Approached by The Independent, the agency insisted it did not recognise the quote cited by the Daily Telegraph, and emphasised that national emergency status is dependent on whether a heatwave is so severe or prolonged that its effects are felt beyond the health and social care system – such as causing power or water shortages – rather than a specific temperature being reached.

The UKHSA’s head of extreme events and health protection, Dr Agostinho Sousa, said: “Heat-health alerts have now been issued to the majority of the country, with temperatures set to remain consistently high throughout the duration of this week.

“Most of us can enjoy the hot weather when it arrives, but it is important to keep yourself hydrated and to find shade where possible when UV rays are strongest, between 11am and 3pm. If you have vulnerable family, friends and neighbours, make sure they are aware of how they can keep themselves protected from the warm weather.”

Heatwaves are the deadliest extreme weather event in the UK, and according to the Met Office there an average of 2,000 heat-related deaths each year.

But scientists have warned that such events will only become more frequent and severe as a result of climate breakdown, and earlier this year the Met Office raised the threshold for weather to be considered a heatwave in parts of the UK to reflect the country’s warming climate.

The highest temperature ever recorded in the UK was 38.7C, reached at Cambridge Botanic Garden in July 2019.

Met Office forecaster Simon Partridge told the Press Association news agency that Sunday holds a 30 per cent chance of seeing that record broken.

His colleague Rebekah Sherwin added: “Weather forecast models are run hundreds of times to determine the most likely weather outcome. For late next weekend and early next week, some runs of these models are allowing exceptionally high temperatures to develop, which is something we’ll be monitoring closely and adding details in the coming days.

“Some models have been producing maximum temperatures in excess of 40C in parts of the UK over the coming weekend and beyond. At longer time scales temperature forecasts become less reliable, so whilst these figures can’t be ruled out, they are still only a low probability.”

Weather extreme enough to trigger a national emergency has the possibility to cause illness and death among the fit and healthy, and not just in high-risk groups, government guidance states.

Disruption to road and rail travel, issues at power stations, higher concentrations of air pollutants, classroom closures and crop failures are among the other risks anticipated during a heatwave severe enough to merit a national emergency, according to the government’s official heatwave plan.