Parts of the UK could be as hot as Ibiza at the weekend, with predicted temperatures up to six degrees above the October average, the Met Office said.
The “unseasonably warm weather” will cover much of the south of England, where temperatures are expected to reach the mid-20s, and possibly even higher, on Saturday and Sunday.
Temperatures could reach 26C in some places in the south-east, making hotter than Athens and Barcelona, which are predicted to hit 25 on the weekend, and similar to Ibiza, which is forecast to reach 27 on Saturday and drop to 26 on Sunday, the Met Office said.
The hottest October day on record was in 2011, when temperatures reached 29.9C in Gravesend. The warmest recorded night was in 1985, in Aber, Gwynedd, in Wales, where temperatures dropped to only 19.4C.
Stephen Dixon, the Met Office spokesperson, said those in the south of the UK will probably experience the “unseasonably warm spell” towards the end of the week and into the weekend.
He added: “That being said, in the next couple of days there are periods of rain moving in from the west on Wednesday, Thursday and Friday.
“There is some rain around as we move through the working week, perhaps those furthest south in England escaping some of those showers.
“In the south-east over the weekend, we could be getting up to 25C, possibly touching 26 in some spots, and feeling relatively pleasant in that sunshine through the weekend in the south with some good spells of sunshine likely as well.”
The unseasonably warm weather is caused by warmer air feeding in from the south, the Met Office meteorologist Alex Burkill said.
Across Scotland and Northern Ireland, it will be increasingly cloudy and wet on Thursday afternoon and into the weekend. It will stay wet in northern parts of the UK, especially across Scotland.
In Glasgow and across parts of west Scotland, heavy and persistent rain is expected on Thursday and Friday and may lead to some disruption to transport and roads, the Met Office said.
In a September heatwave, UK temperatures reached their highest point of the year, with 32.7C provisionally recorded at Heathrow.
The average mean temperature across the country was 15.2C, equalling the previous record set in 2006 – something that would have been “practically impossible” without a human-led climate breakdown, the Met Office said.
The heatwave in England and Wales was the first time since records began that temperatures have been higher than 30C for six days in a row in September, according to the Met Office, helping to make it the UK’s joint warmest September on record.