The figure, from a team at Imperial College London, the Met Office and the London School of Hygiene and Tropical Medicine, is based on what's known about the dangers of extreme heat.
Most deaths will have occurred in the June heatwave, they say - the warmest June on record in England, when temperatures hit 37.7C (99.9F) at Lingwood, Norfolk, smashing the previous high of 35.6C set in 1957.
A rare red health alert was issued for parts of England and Wales at the time, warning even healthy people of the significant risk to life.
