The Environmental Audit Committee has forecast 7,000 heat-related deaths every year in the UK by 2050 if the government does not act quickly.
MPs have urged ministers to act to protect people. Higher temperatures put some at greater risk of dying from cardiac, kidney and respiratory diseases.
Future heatwaves have been forecast to be hotter and more frequent thanks to carbon emissions. The Met Office has forecast UK summer temperatures could regularly reach 38.5C by the 2040s.
The dire warning came as the mercury yesterday peaked at 35C at Heathrow in London, making it the hottest day in the UK so far this year.
Temperatures hit 26C in places such as Edinburgh and Stirling, and 25C in Glasgow and Perth.
ScotRail commuters suffered disruption last night after trains were forced to slow to 20mph on the main Edinburgh-Glasgow line when the rail temperature hit 40C.
The speed restriction was imposed by Network Rail to prevent trains damaging the track near Winchburgh in West Lothian.
Services between Edinburgh and Dunblane were also affected. Several trains were cancelled and others delayed by nearly 15 minutes.
Forecasters said temperatures in the UK could soar to as high as 37C today, triggering a thunderstorm warning into the afternoon. The hot weather has taken a major toll on services across the country.
Cross-Channel rail operator Eurotunnel has cancelled daytrip and overnight tickets for travel today due to “extreme temperatures affecting the shuttle air conditioning”.
Passengers faced five-and-a-half hour queues because of delays caused by the failure of air conditioning units on trains. The Royal College of Nursing said high temperatures were leaving nurses dizzy and exhausted, and 56 fires raged on grass verges next to England’s motorways.
A high pollution alert was issued for London, with fire brigades calling for a ban on BBQs in parks.
The most recent heatwave prior to this summer came in July 2015 when temperatures peaked at 36.7C at Heathrow on 1 July. That temperature is the July all-time maximum record.
There is a chance the high temperatures could even beat the all-time UK record of 38.5C, with the hot weather set to continue into August.
A Met Office spokesman said while it will be a bit cooler and potentially unsettled over the weekend, the hot weather will return next week.