The business model used by the fashion industry is broken and firms need help to adopt more sustainable practices, MPs have been told.
The warning, from a London College of Fashion academic, comes amid increased scrutiny of the UK's fashion retailers.
Prof Dilys Williams, director of the college's centre for sustainable fashion, said legislation and government support were needed.
Marks & Spencer, Primark, Boohoo and Asos have all given evidence to MPs.
(Former Made in Chelsea star Millie Mackintosh gave items to a pop-up "slow fashion" store in east London-Photo Above)
Earlier this month
Prof Williams appeared before the Commons environmental audit committee's inquiry into the sustainability of the fashion industry.
In response to a question from Green MP Caroline Lucas about whether a T-shirt can be produced sustainably for £5.99, Prof Williams said: "If a business is built on fair wages and living within environmental limits then, no, we cannot sell T-shirts at the price that we currently are.
"We are buying 400% more pieces than we were less than 20 years ago... we are spending the money on stuff that we are chucking away.
"The system is broken and it cannot continue as it is. Most businesses know that, but it is about helping them to make that transition to a new form of business."
This era should be seen as a "blip in fashion history", Prof Williams said.
Phoebe English, a south London-based designer, told the hearing that High Street retailers know "their business models are just not sustainable" because young people's shopping habits are changing.
"They will not be going into Primark and coming out with five bags of clothes where garments have cost them five or six quid to purchase and buying multiple clothes - the same clothes in different colours. It is just not how people will be shopping in the future and they know their time is coming up," she said.