Ethical fashion used to be unfashionable. When Livia Firth launched her consultancy, Eco-Age, a decade ago, she says, “it was something no one was talking about”. During the current round of fashion shows – from Extinction Rebellion’s protests to dresses made from recycled plastic bottles – people have talked about little else.

In the last two months, says Firth, “we have turned a corner finally. It is a beautiful moment, but it is also very dangerous. Fast fashion is the first offender in sustainability and there is greenwashing at a level there has never been before”.

Firth is speaking from Milan as she and her team put the finishing touches to the Green Carpet Fashion Awards. Now in its third year, the event focuses on fashion’s social “handprint” rather than its environmental “footprint”, though the two are inextricably linked.

Its aim is to celebrate the unsung heroes making fashion a more ethical business, she says, rattling off a list that includes cobblers and fashion studio staff to the “mayor of a tiny town which is reviving an ancient technique”.

If that makes Sunday night’s event sound low-key, it really isn’t. It’s an Oscars-like production with 1,000 guests and A-list headliners. In the past Donatella Versace and Miuccia Prada have won prizes, while Cate Blanchett and Julianne Moore have presented them. This year the 87-year-old pug-loving designer Valentino Garavani will collect the Visionary award, while the gondoliers of Venice will be applauded for switching to natural fibres for their striped uniforms. The world’s best-known designers will produce gowns, too, working with Eco-Age on looks “according to our principles”.

Firth has been a major player in ethical fashion since 2011, when her husband, Colin Firth, won an Oscar. Gifted with the visibility of being a plus-one for plenty of awards seasons, she chose to wear exclusively ethical brands. At the time ethical style was perceived as a bit of a party pooper, and Firth freely admits: “I could probably have never done it if it wasn’t for Colin and having the opportunity to be on the red carpet.” Through the years, though, things have evolved and people are now more open to speaking, directly, about issues such as exploitation.

In mainstream fashion conversation, though, it is sustainable – not ethical – that has become the hottest buzzword. It says something about human nature that environmental concerns have affected buying habits in a way the human cost alone never quite did, even after the 2013 Rana Plaza tragedy. Then, 1,134 people died after an unsafe building in Bangladesh collapsed. It was the workplace of garment workers making clothes for some of the world’s leading fast-fashion retailers.

Colin Firth and Livia Firth at the Green Carpet Fashion Awards in Milan last year. Photograph: Jacopo Raule/Getty Images

Separating these issues has allowed fast fashion to “appropriate the conversation”, says Firth. Fast-fashion brands have recently pledged to use sustainable materials. But it is the human cost, not the type of fabric used, “which is almost the primary cause of environmental pollution”, she says.

“If they [brands] could not produce so much clothing so cheaply by using slave labour, you wouldn’t have the environmental impact.” Improving fashion’s social cost is something fast-fashion brands “cannot appropriate”, she says, “unless they change their core business model and produce less.

“You cannot make a monster sustainable,” she adds. “The very nature of it is that it’s a monster.”

It’s very different in the luxury space, she says. “We don’t work with all of the brands – but the ones that we do work with make a completely different commitment to what they do because there is a lot of money to invest in research in development.”

One of Eco-Age’s clients, Kering, for example, has been singled out for praise after “investing tonnes and tonnes of money” understanding how to do things differently and introducing an environmental profit and loss statement.

Clearly, Firth’s approach is very different to that of Extinction Rebellion, which campaigned for London Fashion Week to be closed altogether, though Firth thinks the group may have a point.

However, the Green Carpet Awards are more of a carrot to the industry than a stick, being co-run with the chairman of the Italian equivalent of the British Fashion Council. It has its own footprint to be considered, with the plants on the red carpet to be donated to communal gardens in Milan and the green carpet made from recycled fishing nets rescued from the ocean.

Firth has proved that such glamorous awareness-raising works – and she has just found out she has been made an honorary MBE for her efforts. “It will be a weapon of mass construction,” she says. Like being Colin Firth’s wife, or being awarded UN Leader of Change, she says, “it will mean people will listen. Whatever it takes to spread the message.”