Just 20 staff are working on climate adaptation within a key government department tasked with protecting the environment and maintaining food security, a freedom of information request has revealed.

The officials make up 0.3% of staff within the Department for Environment, Food and Rural Affairs.

The government has been warned by the climate change adaptation committee that it is lagging far behind in terms of adapting to a new climate as a result of global heating.

The climate crisis is increasing both summer heatwaves and winter rainfall in the UK, with both drought and flooding more likely.

Peak river flows could increase by up to 45%, while water supply shortfalls may surpass 5bn litres daily, the committee has warned. It said the economic cost of failing to adapt could be between 1% and 5% of UK GDP annually by 2050 – £60bn to £260bn a year.

But only 20 staff out of 6,613 in Defra are working on climate adaptation, according to the data.

“England is desperately unprepared for the impacts of the climate crisis, and these shocking figures show how few officials are working on the problem at the top of government,” said environmental writer and campaigner Guy Shrubsole, who obtained the data.

Shrubsole called on the new environment secretary, Angela Eagle, to seize the moment amid heatwaves and wildfires to greatly boost staffing and funds for climate adaptation.

“Andy Burnham has seen the effects of climate change in Makerfield, which flooded in past winters, and as Manchester mayor when wildfire smoke from Peak District grouse moors choked local residents,” he said. “It’s time he levelled with the country about the climate emergency and set out a radical plan to get us off fossil fuels and prepare communities for extreme weather.”

The data is revealed as Burnham is being challenged by the Wildife Trusts and other leading environmental NGOs in his first 100 days in office to reset the government’s approach to the environmental emergencies facing the UK. They want him to recognise that ecological restoration – such as rewetting bogs and managing natural flood defences – is essential to national security and public health.

Since taking office Burnham has not mentioned the climate crisis, the extreme heat the UK is experiencing this summer, the wildfires that have taken hold from the south-west to the north of England, nor the drought covering almost three-quarters of the country. The UK is about to enter its fifth heatwave of the summer, as climate breakdown makes extreme heat, drought and wildfires more likely.

Friends of the Earth’s head of policy, Mike Childs, said: “The UK is in the grip of a growing climate crisis. Across the UK communities are under attack from relentless heatwaves, droughts and wildfires, putting lives, homes, farmers and nature at risk.

“Andy Burnham must end his silence on the climate emergency and pledge to make it a top priority by strengthening plans to protect communities from increasingly frequent and extreme weather – especially those most at risk.

“But we must also tackle the cause, not just the consequences. The government must do more to cut the pollution driving climate change by accelerating the shift to clean energy and ruling out new oil and gas developments like Rosebank and Jackdaw, and a third runway at Heathrow.”

Firefighters across the country are tackling record levels of wildfires – with 966 this year, including 458 in July alone. Steve Wright, the Fire Brigades Union general secretary, is calling for 5,000 more firefighters to be recruited, saying it should be a national priority to have enough properly equipped firefighters to face the threats of climate extremes.

The UK is short of much of the key equipment to tackle wildfires that European fire fighters possess. The country does not have any dedicated fixed-wing water-bombing planes or specialist aerial firefighting aircraft.

On Wednesday, No 10 announced Burnham would chair an emergency Cobra meeting in response to the extreme heat.

The prime minister will meet ministers, officials and agencies as high temperatures continue across the UK, with temperatures of 33C forecast on Wednesday and up to 38C on Thursday.