Britain could see the highest September temperature in more than 50 years, according to the Met Office.
Tuesday’s thermometer readings could rise to between 30C and 32C (86-90F) in the south-east, while further north, Scotland should still see an above-average 20C-21C.
It’s ten years since UK temperatures rose above 30C in September, when London experienced a high of 30.5C, but if the peak heat is above 31.6C, as it was at Gatwick on 2 September 1961, that will break the 55-year-high.
However, it would take a freak heatwave to set an all-time record - in 1906, a temperature of 35.6C was recorded at Bawtry, in South Yorkshire.
The Met Office’s Simon Partridge said: “Basically, we’ve got air coming up from the south. The origins of this air is generally southern France and northern Spain, where things are fairly warm at this time of the year. So we’ll start to see things warming up.”
Above average temperatures can be expected across the UK for the rest of the week, he added.
However, conditions will become more unsettled on Thursday and Friday, with rain sweeping east. This unsettled weather will continue into next week, when the north-west will be subject to bands of rain interspersed with dry spells. But the south-east will benefit from higher pressure over Europe and subsequent drier, warmer and more settled conditions.