Climate groups and unions joined forces at a protest outside Tata Steel’s London headquarters on Monday where they handed the firm an open letter calling for a “just transition” that protected workers.

A group of representatives from organisations including Greenpeace, Extinction Rebellion, Community Trade Union (CTU) and Trade Union Congress (TUC) gathered outside the offices.

They held banners which read “Save our steel” and “In solidarity”, before posting the letter through the building’s letterbox.

The group was calling for alternative solutions to decarbonising Tata’s Port Talbot plant in south Wales in order to prevent mass job losses.

We firmly support the workers’ demands for a just transition that secures future-proof decarbonised production while protecting jobs

The firm shut down one of two blast furnaces at the plant, with the second due to be shut in September under plans to switch to a greener method of steel production, which requires fewer workers.

Unions are opposed to the changes, which will lead to the loss of around 2,800 jobs, although Tata has argued its restructuring programme is designed to stem “unsustainable” losses of more than £1 million a day.

Tata has said it would make every effort to mitigate the impact of the transformation on affected employees and the local community.

In the letter, a coalition of climate groups said the new Labour government brought an opportunity to renegotiate for a fairer and greener transition in the steel industry.

It read: “We firmly support the workers’ demands for a just transition that secures future-proof decarbonised production while protecting jobs.

“Tata Steel’s current plan would see thousands of jobs lost, and be devastating for communities in South Wales and beyond.”

The letter warned that closing down the blast furnaces without immediate replacement would “simply offshore our emissions” by leaving the UK reliant on importing dirty steel from countries such as China and India.

At the protest, the groups argued for keeping the blast furnace open while transitioning workers gradually and adopting new technologies, such as hydrogen-based steel making and open slag bath furnaces.

Paul Morozzo, Greenpeace UK climate campaigner, said steel was essential for the green transition, including wind turbines and electric vehicles.

Speaking to the PA news agency, he said: “Workers and the work that are absolutely central to the transition should be supported through it and as part of it and that is the only way you can have a proper transition.”

Mr Morozzo added that it would be a “massive contradiction” if the green movement did not support workers.

We just need a bit of longevity for that furnace to stay alive for a bit longer so we can transition people and bring them along for the ride. Otherwise, people are just seeing the transition as negative ...

“One of the reasons we care about climate change is because we care about people,” he said.

“If the very act of trying to solve climate change can ruin a whole load of people’s lives and communities and throw people on the scrap heap, that would undermine the very principles we support in the first place.”

Former steelworker Alun Davies, from CTU who worked at Tata for several years, warned that closing the furnaces quickly was the “wrong decision”.

“We understand that we have to decarbonise,” he told PA.

But he added that there had been “a blatant disregard for people” in the way Tata Steel was trying to adapt to lower carbon practices.

He described how friends had been “breaking down” due to stress, while other workers had been “struggling to come to terms with losing their job”.

“We just need a bit of longevity for that furnace to stay alive for a bit longer so we can transition people and bring them along for the ride,” he said.

“Otherwise, people are just seeing the transition as negative – it’s destroying their lives, it’s destroying their families and that’s the opposite of what it can be.”

Mr Davies said there were other options but that Tata Steel was not willing to consider them “because it’s too costly and it eats into the profit”.

“We understand at the moment they’re losing money, but with a greener transition they would make money but over a longer period of time,” he said.

On behalf of the steelworkers’ union, the letter’s signatories, which included more than 30 groups such as Friends of the Earth, Green New Deal Rising, and E3G, outlined several demands.

They called on the Government and Tata to commit to maintaining production and jobs at scale, negotiating with unions on transition plans and ensuring no compulsory redundancies.

Decarbonisation does not mean deindustrialisation, and we will be working to safeguard jobs as part of these negotiations, securing the future of steelmaking communities for generations to come

The Labour governments in Wales and Westminster have also been pushing Tata not to pursue any compulsory redundancies, with promises of £3 billion in extra funding for the steel industry in the UK.

A Department for Business and Trade spokesperson said: “Steel is vital for a vibrant, secure economy. Our steel sector needs a government working in partnership with trade unions and business to secure a green steel transition that’s both right for the workforce and delivers economic growth.

“Decarbonisation does not mean deindustrialisation, and we will be working to safeguard jobs as part of these negotiations, securing the future of steelmaking communities for generations to come.”

PA has contacted Tata Steel for comment.