Last month was the UK's joint warmest September on record after a late summer heatwave saw temperatures soar above 30C.
Provisional figures by the Met Office show the mean temperature was 15.2C, equalling the previous record set in 2006.
It means five of the top ten warmest Septembers have taken place this century.
The heatwave in the first half of the month saw many places with temperatures above 30C, peaking at 33.2C at Kew Gardens in London on September 9 – the hottest day of the year.
It is only the fifth time the Met Office has recorded the hottest day of the year in September.
Met Office scientific manager Mark McCarthy said: "It also had seven consecutive days where temperatures were above 30C somewhere in the UK, which had never happened in this month in Met Office observations.
“The significantly warm start to September was influenced by high pressure across Europe. This helped to draw warmer air over the UK at the start of the month.
“Once this pattern subsided, we had a more Atlantic influence, with periods of winds and rain, as well as Storm Agnes late in the month, yet often a south-westerly flow resulting in above average temperatures but also humid conditions and plenty of rain.”
A change in the weather in the second half of September saw storm Agnes bring strong winds and heavy rain to parts of the country, meaning the month ended up wetter than average.
After battering Ireland, the storm died down before it caused any major damage in the UK, despite some earlier warnings.
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