Hundreds of thousands of Londoners face having to retrofit their loft conversions as temperatures soar in coming years, a new report is warning.

Sir Sadiq Khan and London Councils published the study which outlined how the capital needs to adapt to the growing climate crisis.

The string of recent heatwaves have laid bare the scale of the threat facing the city.

“We must create cooler homes and buildings, greener and shadier neighbourhoods, and infrastructure that can withstand a hotter climate,” Sir Sadiq stressed.

Loft conversions have been specifically identified by City Hall as a priority housing type for overheating retrofit.

The Heat Ready London Technical Report, commissioned by the Mayor, told how climate-related damage could cost the capital up to £36 billion a year by the 2050s.

More than half of homes in Britain already experience overheating risk, it explained.

Without adaptation, under a high-emissions warming scenario for 2C warming in 2050, the overheating risk in a typical summer is projected to result in up to 10,000 excess heat-related deaths in the UK.

The May and June heatwaves alone are estimated to have killed 1,000 Londoners.

Indoor overheating, the report added, is the primary causal exposure for most heat-related premature deaths and ill-health.

“With 92 per cent of residents in all existing homes affected by heat risk, it is critical homes are retrofitted to be heat-resilient,” the study said.

Highlighting the varied housing stock across London, it added: “Some archetypes such as top-floor flats, loft conversions, bungalows and highly insulated and glazed homes have higher risk of overheating.

“The variation in stock requires a flexible approach to retrofit, which allows for a diversity of solutions to be implemented.”

The report proposes that loft conversions are included in a wider programme to retrofit London's highest-risk homes.

Measures which could be used include:

* In some cases active cooling/air conditioning

* Secure purge ventilation to rapidly remove air or pollutants

* Insulation designed as part of an overheating strategy

Hundreds of thousands of Londoners have extended their homes upwards, with loft conversions, over the years.

The trend was fuelled by soaring house prices in the capital, and partly by rises in stamp duty imposed by former Chancellor George Osborne more than a decade ago on more costly properties, which made it more expensive for some people to move in parts of London.

Many of the new loft rooms have high quality double glazing to keep in the heat during the autumn and winter.

But as temperatures are now soaring regularly above 30C during the summer, they are also retaining the heat which rises in homes into the loft area.

So, many Londoners now face having to retrofit their loft conversions or put up with unbearable heat in future years.

Sir Sadiq said: “The climate crisis is on our doorstep.

“It is already threatening Londoners’ lives, disrupting vital services and costing our economy hundreds of millions of pounds.

“Without further action, climate change could cost London as much as £36 billion a year by the 2050s.”

The report also outlined how lost productivity linked to high temperatures is estimated to cost London £577 million a year.

The study is the technical basis for Heat Ready London, the capital’s first city-wide heat plan, published in June which identified 37 priority actions.

The plan showed how around one million London homes are at risk of overheating, alongside 1,361 schools, 60 hospitals and 351 care homes in areas most vulnerable to extreme heat.

It proposed a series of measures including boosting health services to deal with heat incidents, making public transport more resilient, making homes and workplaces cooler, more cooling spaces, trees and public drinking water.

The danger to Londoners is not limited to days of extreme heat, the research stressed.

About 90 per cent of heat-related deaths in London happen when temperatures are between 24°C and 32°C.

Evidence also suggests Londoners aged between 45 and 65 face a greater risk of dying during hot weather than people of the same age nationally.

Commuting to work on the Tube and other public transport may be a factor in this finding.

The Mayor has faced criticism for not doing more to introduce air conditioning more quickly across the Tube network.

Plans for new air-conditioned trains on the Piccadilly line and DLR have been hit by delays.