The sales floors of Selfridges on Oxford Street in London are not typically places shoppers expect to bag a bargain. But a new space in the high-end department store is dedicated to buying and selling secondhand clothes and accessories, with a rack where people can drop off their used items.

The major difference between the concession run by Vestiaire Collective and hunting through secondhand clothes at the local charity shop, is the brands on offer – Mulberry handbags for £465 and a Tom Ford suit for more than £4,000 among them. But its existence is testament to the growth in “preloved” or “preowned” fashion.

Recent years have seen a boom in the number of people buying this way – this year the area is expected to grow by 12%, compared with 3% in the regular luxury goods market.

The reason is, in part, simple – people can buy designer goods at lower prices. But its popularity is also down to a higher emphasis on sustainability.

A study by the Boston Consulting Group found the preloved market was “moving into the spotlight” and any stigma about wearing secondhand had gone as more consumers were rejecting fast, disposable fashion.

“The fashion industry is one of the most polluting in the world and consumers increasingly understand that extending the life of a garment has a big positive impact,” says Cecile Wickmann, founder of resale website Rebelle.

There is now a glut of websites selling secondhand designer brands at discounts of up to 70% of the original retail price, among them Hardly Ever Worn It (HEWI), Videdressing and Designer Exchange, with hundreds of brands for women. The men’s market is growing too, with trainers and watches in high demand.

Typically, websites take a commission on sales between 18% and 30%, depending on the value of the item. Most are inspected and verified as genuine by the websites’ fashion experts before they are sent out.

Fanny Moizant, who co-founded Vestiaire Collective 10 years ago, has noticed a shift in emphasis among users. “It used to be that people were looking to access luxury brands at a cheaper cost and it was the lower price tags that were the primary motivator. Now, I would say, consumers are driven by a desire to shop more ethically and this is particularly true among younger consumers.”

Amy Fyfe, co-founder of boutique and online market editsecondhand, agrees. “People come into the shop and say they are not buying anything shop-new this year. There is a money-saving element, but it is usually about shopping ethically and not creating so much waste.”

While there are savings to be made, prices can also be eyewateringly high. Recently, buyers could pick up a Gucci Soho “disco bag” in red leather on Vestiaire Collective’s website for £583. The exact same crossbody bag – direct from Gucci – sells for £805.

However much she likes high-end fashion, personal trainer Jen Brown, who set up her fitness business for women, One Fit Mother, 10 years ago, can’t justify paying the high prices. Buying “preloved” resolves that problem and settles her desire to be sustainable. “One of my favourite purchases has been these J Brand black jeans,” she says.“I got them for £70, but new I think they’d be about £260. I have also recently picked up a pink Isabel Marant jumpsuit for £80, which would sell for around £400 new. All the items are in amazing condition – almost new.”

Quality wool coats by designer Isabel Marant cost from about £450 when new, but shoppers can pick up one preloved from about £100. And a new Dior Saddle bag in denim canvas would set you back a cool £2,700, yet shoppers willing to fork out £419 could buy a very similar grey version at HEWI.

Handbags typically sell quickly, particularly if they are current or from recent designer collections. In some cases, a handbag with a blue-chip name – Chanel or Hermès, for example – may even appreciate in value. This is because, for some styles, it is difficult or impossible to find exactly the same item in the primary market. When demand is high, limited or rare, prices rise.

Sharon Wolter-Ferguson of HEWI says attitudes to ownership have changed. “People are much more comfortable with buying something, wearing it once or twice then selling on – perhaps using the resale to fund their next purchase.

“It is more like rental. In many cases the stock on our site is new with tags, where someone has been given something, or bought it in the wrong size, or simply never worn it. Most items are from recent collections, so shoppers are getting a bargain.”

Fakes are a menace, however, and consumers need to be on their guard. Reputable resale websites check and verify items are genuine before or after a sale, but some charge a fee to the seller or buyer for this.

They will also clearly list their returns, payment and dispute policies and have full contact details in case of problems.

Consumers should also be aware that on resale sites they are buying and selling from each other, rather than from the business, so things can go wrong, and people should be aware of the risks and protections that are available.

“Always ask yourself: can you trust who you are buying from? This market is all about trust,” says Moizant.

Also, preloved designer clothing is mostly available in smaller women’s dress sizes – a six or eight for example. Wolter-Ferguson admits most designers do not offer items above a UK 14, so will be harder to find. “There is a greater focus in this market on smaller sizes,” she says.

Deal … or no deal?

• Deal or trade through a business you trust – whether it is a physical shop or online. Make sure it has contact details and a disputes policy if things go wrong.

• Research the market before parting with any cash. If there is a designer brand you love, or a specific style, then find out the price it usually sells for – new and used.

• If you are looking for an investment piece that might hold its value, opt for “blue-chip” names – Burberry, Chanel, Gucci, Louis Vuitton – that have stood the test of time.

• Handbags are always in demand. Look out for classic styles and colours that will have wide appeal if and when you choose to sell.

• Most resale websites will offer an app or text and email alert service if you are waiting for a particular item to become available. Act fast when items come up.

• Once you have your treasured dress or bag, consider how to store it and protect it from dust and moths. If you want it to retain its value, it is important to look after it.