It’s one of fashion’s best kept secrets, a website where you can buy luxury brands such as Burberry, Prada and Miu Miu as well as the best of the high street for a steal.

Sales were up 33% at Christmas as shoppers bagged vintage and designer clothes for the party season but the company is not listed on the stock exchange like the web giant Asos and there is no chance of it ever being taken over. And if you look closely some of the clothes might seem familiar.

In fact they might actually be your clothes – because Oxfam has emerged as an unlikely rising star of the UK’s fast-growing online fashion scene as it casts an increasingly canny eye over the branded cast-offs and vintage styles dumped in bin bags on its shops’ doorsteps every day.

“It is a big secret but when people hear about our website they are really intrigued,” says Oxfam trading director Andrew Horton who wants to double the size of the web operation to reach 10% of retail sales over the next three years.

The website is run out of a cavernous warehouse in Batley, West Yorkshire. The building is home to Wastesaver, the charity’s sorting and recycling centre, where every week 50 paid staff sift though 80 tonnes of clothing delivered to its door.

“The shops get donations every day,” explains Horton. “If we don’t have the logistics in place to collect donations they can get clogged up. Some shops only have small stock rooms and we don’t like to turn donations away.”

The 80,000 sq ft warehouse, which is a short drive away from web giant Asos’s hub in Barnsley, receives drops of clothing every weekday. The bags are tipped on to conveyor belts which pickers scan for the most saleable items, dropping them into white sacks labelled by category “shoes”, “retro”, “leather”. There is also a second sorting centre in Milton Keynes.

The sacks are then passed on to a small team who are surrounded by moodboards created by fashion students which alert them to the latest trends so that they can select them for the online shop. Duster jackets and ponchos are expected to be very big in 2018, along with graphic bags, leather gloves and anything in acid yellow.

There are more than 125,000 one-off products listed on the Oxfam website, a vast catalogue that includes books as well as music and clothing. At Christmas the most searched for brands on the website included Barbour, Gucci, Whistles and Boden. At the moment a trawl of Oxfam’s designer boutique turns up a silk Hermès scarf, with a £190 price tag, and a Burberry trench coat for £110.

“I was in Batley to help pack Christmas orders and one was a Karl Lagerfeld jacket from the 80s,” says Horton. “We always take the view that people who donate want us to try and raise as much money as we can. Generally that’s about a third of the retail cost. The Lagerfeld jacket was £75 and people who like vintage clothing will know that is a good price.”

Pickers have to spot the most saleable items. Photograph: Lorne Campbell/Guzelian

The site’s fashion credentials were boosted by Oxfam’s first catwalk show at London fashion week in 2017 where models paraded the cream of its “preloved” clothes. The charity is repeating the exercise this year with stylist Bay Garnett currently assembling the collection.

In the neighbouring warehouse to Wastesaver a team of volunteers is tasked with giving the clothes the Asos treatment, by photographing them on mannequins and uploading their descriptions on the website.

About half of Oxfam’s 620 stores perform this task themselves and the charity is investing in technology to speed up what is a time-consuming process.

Some of the desirable items unearthed by Wastesaver staff are sent back to shops that don’t receive enough donations, including branches in Cleveleys, Guisborough and Bury. More outlandish items, and anything screaming fancy dress, are saved for Oxfam’s festival pop-up shops at Glastonbury and Bestival.

Just 3% of the clothes sorted in Batley are returned to stores or sold online with the remainder diverted overseas or recycled. The summery stuff in decent nick, plus any old bras, is rolled up into hay-style bales and sold to Frip Ethique, Oxfam’s west African social enterprise.

Wastesaver staff members take a break to try out some of the clothes before they are processed. Photograph: Lorne Campbell/Guzelian

Winter clothes that UK shoppers may dismiss — such as supermarkets’ own brands which are almost as cheap to buy new — are packed off to eastern Europe.

For clothes that have reached the end of their wearable life the future is shoddy rather than shabby chic. Oxfam sells its leftovers to recycling companies who turn them into the cheap woollen yarn used to make carpet underlay or car seat linings.

It was a tough Christmas for the UK retailers but Oxfam recorded like-for-like sales growth of 1.6%. Total sales were up 1.2%, raking in £16.9m in the eight weeks to 23 December.

The figures are a drop in the ocean compared with high street giants such as Marks & Spencer but with annual sales on track to exceed £74m this year, Oxfam’s success is measured not by its share price but clean water, with its progress at Christmas enough to help 200,000 people in an emergency.

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