Scientists expect powerful heatwaves such as the one that hit continental Europe in 2003 to be commonplace by the 2040s.
But there is no evidence winters will become generally milder, say the experts. Despite the summer heat, people will still have to plan for the occasional very cold winter, as occurred in 2011.
There is now good evidence that climate change is stoking up warmer summers in the UK, according to the Met Office.
Observations over the past 10 years suggest that by the 2040s more than half of summers are likely to be hotter than 2003.
More than 20,000 people died in the record-breaking heatwave which peaked in August 2003, the hottest spell in Europe for 500 years. Summer 2003 certainly had an influence in the UK," said Professor Stephen Belcher, head of the Met Office's Hadley Centre. "By the 2040s we can expect events like 2003 to be normal."
Rainfall trends were harder to track, he said, but there were signs that heavy downpours were becoming more frequent in the UK, a pattern likely to be linked to climate change. On the other hand, the recent series of soggy British summers was thought to be due to natural climate variation. "Heavy rain is becoming heavier and that's consistent with our picture of a warming world and warming atmosphere," said Prof Belcher. "
Looking at rainfall intensity, what would have been a one-in-125 day event in the 1960s or 1970s was now a one-in-85 day event.
The scientists concluded: "The UK has seasonal weather that varies hugely. Nevertheless, human influence has been detected in the hot temperatures in Europe during summer 2003, and there are signs that the character of rainfall has shifted in the past 50 years with more heavy rainfall events, consistent with a warmer atmosphere holding more water."