Sweltering temperatures of up to 40C could be a regular occurrence in the UK by 2100 if carbon emissions stay very high says the Met Office.
The current record stands at 38.7C, set in Cambridge last July.
This new study says there is an "increasing likelihood" of going beyond this figure, because of the human influence on the climate.
Under the worst emissions scenario, the 40C mark could occur every three and a half years by the end of this century.
The past two summers have seen periods of significant and uncomfortable heat across much of the UK and Europe.
Met Office researchers are clear that these hot summers occurred partly as a result of warming gases originating from human activities.
In fact, the use of energy, transport and all the other carbon that we've been producing made the heatwave of 2018 around 30 times more likely.
The Met Office's new modelling study says that this human influence on UK temperatures is going to continue.
"We find that the likelihood of extremely warm days in the UK has been increasing and will continue to do so during the course of the century with the most extreme temperatures expected to be observed in the South-East of England," the report finds.
The scale of the impact, though, is still very much in our hands.
Right now the chances of any part of the UK hitting 40C are extremely low - it could occur once every 100 to 350 years.
This changes significantly by the end of the century, depending on how much more carbon is emitted.
The researchers say the chances of hitting that high mark are "rapidly accelerating" with a 40C day occurring every 3.5 years, under a very high emissions scenario.
Under a more modest carbon projection, the 40C mark happens about once every 15 years.
"If we think about the climate that we would have had, had we not emitted any greenhouse gases, and something like 40C looks looks well nigh impossible, because it is so extreme," said Prof Peter Stott from the Met Office, one of the paper's authors.
"But now we've already entered this scenario where we can see over 38C as we saw last summer, and increasingly the chances of seeing 40C become ever higher if we continue emitting greenhouse gases," he told BBC News.
Some experts question the use of the most extreme carbon emissions scenario as being unrealistic.
Prof Stott says that both the very high and the medium carbon projections used show a considerable chance of hitting 40C, and even the lower estimate significantly increases the chances of 40C compared to the present.
Even if the mercury doesn't go beyond the 40C mark, consistent high temperatures would have serious implications for elderly people.
"I think the main risk really is to vulnerable people, particularly elderly people who are vulnerable to such extremes," said Prof Stott.
"And when we're looking at extremes that we haven't seen before, then it's something to take very seriously because the buildings, the care homes, the homes that people are living in, are not necessarily adapted for such temperatures."
The chances of hitting 40C are more likely in the South East of England, with temperatures above 35C becoming an almost annual occurrence by the end of the century.
But traditionally colder parts of the UK will also see a hike in temperatures, with many areas of the north exceeding 30C at least once per decade.
Co-author and head of the Met Office National Climate Information Centre Dr Mark McCarthy, said: "This research shows human-caused climate change has set us on a course to see temperature extremes in the UK that would be highly unlikely under a 'natural' climate, although urgent action to reduce emissions now can significantly reduce the occurrence of extreme high temperatures in the UK in the future.
The study finds that if the world reduces carbon emissions in line with the Paris climate agreement, then the chances of hitting these dangerous temperatures are significantly reduced.
The research has been published in the journal, Nature Communications.
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