Transforming the energy efficiency of every home, mass rewilding of the countryside, huge investment in cycling, walking and buses, and a “frequent flyer” tax are among a raft of green policies being put forward by the politicians vying to replace Jeremy Corbyn as leader of the Labour party.

In answers to 17 questions put by the Guardian before the coronavirus outbreak, all three remaining candidates – Rebecca Long-Bailey, Lisa Nandy and Keir Starmer – set out detailed plans on how they would go about tackling the dual environmental crises of climate breakdown and mass extinction, and shed light on how the party under their leadership would tackle some of the biggest challenges facing the UK, and the world.

In the 2019 election, the climate crisis was more prominent than it has been in any previous contest, and voters and green campaigners are increasingly putting pressure on the leadership candidates to stick to the ambition of the Labour manifesto, which for the first time put tackling the climate emergency at the heart of its offer.

Earlier this year, the Labour for a Green New Deal group, which campaigned for the party to adopt a radical economic plan to deal with the crisis in the run-up to the election, sent five questions to each candidate and scored their answers out of 10: Long-Bailey came out on top, with Starmer second and Nandy third.

The Guardian also scored all MPs on their record on the climate crisis as part of The polluters series last year. In that analysis, Long-Bailey and Nandy both came out with the maximum score of 100%. Starmer had only been present for two votes, meaning there was insufficient information for him to be given a score.

In a clear sign of how deeply embedded a radical environmental agenda has become in Labour policy, all three candidates, answering before the Covid 19 outbreak said the climate crisis was the biggest challenge facing the UK. Both Long-Bailey and Nandy highlighted their previous experience – Long-Bailey as the architect of Labour’s Green New Deal at the last election and Nandy from her time as the party’s shadow energy secretary and her role leading Labour’s team at the Paris climate talks in 2015.

The Green New Deal

All the candidates pledged broad support for Labour’s comprehensive Green New Deal agenda. Both Long-Bailey and Starmer supported the specifics of the plan set out in the 2019 manifesto, spelling out how the UK could rapidly decarbonise the economy and create hundreds of thousands of secure, unionised green jobs.

Starmer said the project should be “hardwired” into everything a future Labour government did “from foreign policy to local government, from transport to housing”, and he flagged up the role of the “green transformation fund and a national investment bank” to pay for it.

Long-Bailey said that under her leadership Labour would organise and pay for such an ambitious scheme through public ownership and investment in the energy system to ensure “extra costs are not loaded onto homes that can’t afford it”.

Nandy did not commit to the details of the plan but agreed there needed to be “a wholesale transformation” in the way homes and businesses were powered and heated, adding that “this is possible and necessary and offers huge economic opportunities”.

Public transport

Asked whether they would commit to greater funding for public transport, cycling and walking than for road building, Long-Bailey said she would, saying it was necessary not just to tackle the climate crisis, but to improve “our economy, the connections between cities and towns, and rural areas, making our public transport more accessible and to encourage healthier lives and cleaner air.”

Neither Nandy nor Starmer specifically committed to spending more on public transport, walking and cycling than roads although both said they would increase investment in those areas.

Nandy said she would nationalise the railways and hand over control of buses to local councils so they were run “for people not profit”.

Starmer said the government had made a “political choice to spend transport budgets on roads rather than greener and cheaper forms of transport”.

He added: “I would lead a Labour government with different priorities: building a more sustainable, affordable, accessible and integrated transport system – with investment in bus services, renationalisation of our railways, and support for cycling and pedestrians.”

Airport expansion and frequent flyer tax

All the candidates expressed interest in a frequent flyer tax to ensure that the 15% of wealthy UK residents who are estimated to take 70% of domestic and international flights pay more for the environmental damage they cause.

Nandy said she would look to “make the system fairer and greener”. Long-Bailey said it was right to “ask wealthy frequent flyers to shoulder more responsibility, or reduce the frequency of their flights”.

Starmer said the tax system should encourage people to use alternatives to flying.

All three said they were opposed to expansion at Heathrow and were sceptical about aviation expansion elsewhere in light of the UK’s legal commitments to reduce carbon emissions.

Nuclear power

None of the candidates came out against nuclear power. Long-Bailey said she supported it where necessary for the UK’s “energy security”. Nandy said that the middle of a climate emergency was the wrong time to rule it out definitively. Starmer said nuclear power should be “part of the mix” in the transition away from fossil fuels, but the “overwhelming focus” should be on renewables.

Red meat

Asked whether they would support policies to reduce red meat consumption, Nandy said the focus should be on the fossil fuel industry. “The priority for governments must be to focus on the biggest driver of emissions, which is the global fossil fuel industry; but the Committee on Climate Change has made it clear that we also need to think about how we manage our land and produce our food.”

Long-Bailey highlighted the growing number of people who are cutting down on red meat “as people think about the environment and their health”, but stopped short of any specific policy commitments.

Starmer acknowledged that the meat and dairy sector was “one of the most significant contributors to climate change and, in many countries, deforestation”, adding that everyone should think about how to reduce their consumption.

But he added: “Changes in behaviour, important as they are, should not distract us from the systemic nature of the problem of climate change.”

Rewilding and biodiversity

Nandy said tackling the climate emergency went “hand-in-hand with restoring our natural environment”. She backed Labour’s existing policy of creating 10 new national nature parks, adding: “I would also enable more people to take control of the management of their local parks, and ensure that local government had the powers and funding to maintain them.”

Starmer agreed rewilding was an essential part of the “fightback against the climate and environmental emergency”.

“I support ambitious tree-planting schemes and new nature parks to halt the devastating loss of biodiversity and to help in the fight against air pollution which plagues our streets.”

Long-Bailey also backed Labour’s existing plans to create new parks and rewild existing ones, as well as “natural corridors” across the country.

“These are examples of actions we need to take to tackle the climate crisis, but will also make our cities, towns and local communities nicer and healthier places to live, bringing public luxury to the spaces and services we care about.”