Temperatures could reach the mid-20s this weekend as "significantly warmer air" moves in, according to the Met Office.
October started on a high with 24.1C (75.4F) recorded at Wisley in Surrey on Sunday - and similar conditions are set to return in the coming days.
Met Office forecaster Alex Deakin said:
"As we go through the week, the high pressure tends to drift further eastwards; we could waft up some warmer air - some significantly warmer air - by the time we get to Friday and in to Saturday."
London is expected to approach the mid-20s on Saturday and Sunday under clear, sunny skies - with low-20s in Manchester, Birmingham and Cardiff.
It is likely to be cloudier further north, but still pleasant - with the Met Office forecasting 21C (69.8F) in Belfast on Saturday and 19C (66.2F) in Glasgow.
Before then, however, it will be fresher and wetter for many.
It comes as the Met Office said last month was provisionally the UK's joint warmest September on record.
September's provisional average was 15.2C (59.4F) - the joint warmest in a series that goes back to 1884 - and the same as 2006.
The Met Office said this was "substantially influenced" by the impact of climate change, with the heatwave in the first half of the month boosting the average.
September, which was also wetter and sunnier than average, had seven consecutive days with temperatures above 30C in the UK - the first time this had happened for that month in Met Office records.
(c) Sky News 2023: UK weather: Summer-like temperatures on the way - after joint warmest September on record
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