All new UK homes should be built with air conditioning to cope with the effects of the climate crisis, according to the Liberal Democrats.

The party says British homes are dangerously unsuited to rising temperatures, meaning passive cooling measures such as planting more trees in residential areas are necessary.

The Lib Dems also want air conditioning to be mandatory in essential public buildings such as schools and health facilities.

The problem of overwarm homes has been highlighted by a UK Health Protection Agency yellow alert for high temperatures to run from Tuesday morning until Friday morning for the south-east, south-west and east of England, the Midlands, and Yorkshire and the Humber.

Temperatures in London are forecast to reach 32C (90F) on Wednesday, before cooling. Some other parts of the UK will be wet with notably lower temperatures.

As well as being hot, much of the summer has been exceptionally dry. In July so far, there has been just 5% of the average rainfall across England, falling to 1% in the south, bringing droughts and severe risk of wildfires.

The Lib Dems’ “climate ready” programme would make it a legal requirement for new homes to have either air conditioning or another cooling system. They say this is especially important for older people or those in poor health.

The number of UK homes with air conditioning has doubled in the past three years amid rising temperatures, according to industry estimates. However, this still comes to only about 4m of the estimated 30m-plus homes in the country.

According to polling commissioned by the Lib Dems, 28% of people said they had bought a fan or an air conditioning unit during the recent heatwaves, with 26% of respondents saying the conditions had left them feeling unwell or faint.

Tim Farron, the party’s environment spokesperson, said: “This latest set of relentless heatwaves has taught us that Britain is woefully unprepared for extreme heat, and families across Britain are paying for the cost of inaction.

“With another heatwave on the horizon, the government must step in with a new plan that takes the onus off already-struggling Brits and commits developers to build homes fit for the future – insulated properly and equipped with air conditioning.”

Gideon Amos, the party’s housing spokesperson, said: “Air conditioning is becoming essential in UK homes, which are now among the smallest and hottest in Europe after previous Conservatives governments swept away minimum space standards.

“Andy Burnham must see sense and enable the country to adapt fast – looking at how we build well for the future so that we give our society the security needed during these devastating heatwaves.”

The heatwaves of May and June, during which there were an unprecedented three successive days of red warnings for extreme heat, killed about 2,700 people, with a peak fatality rate of about 440 people a day, according to an analysis led by Imperial College London.

The statistics illustrate the increased risk from extreme heat exacerbated by human-created global heating. More than 40% of the people affected would not have died without the 1.4C of human-caused heating to date, according to the analysis.