The multibillion-pound clothing retail group Arcadia, which runs some of the UK high street’s biggest names, including Topshop, Miss Selfridge and Dorothy Perkins, has sent retrospective payments worth hundreds of pounds to dozens of its former unpaid interns.

Interns who worked at Arcadia’s head office in London said they have received cheques for their labour up to a year after their placement with the company’s PR department ended.

Arcadia had been using dozens of unpaid interns to ship clothing back and forth to media contacts from a “windowless” stockroom, former interns have told sources in the UK.

Arcadia’s move comes as HM Revenue and Customs has been putting pressure on the fashion industry to enforce the minimum wage and rid the sector of a culture of unpaid labour.

HMRC told the Guardian it has brokered a deal with the fashion industry to make sure it complies with national minimum wage legislation, which states that over 21s who work must be paid at least £6.08 ($9.40) an hour.

Over the past few months HMRC enforcement officers have visited scores of designers and fashion houses to perform “health checks”, making sure all workers, including interns, are paid what they are legally owed, the Guardian understands.

The health checks are being carried out in conjunction with the industry body, the British Fashion Council, which has welcomed the move on Wednesday, saying: “The fashion industry provides access and opportunities to many young people, and the BFC aims to ensure that these valuable opportunities can continue in a legal framework.”

In correspondence with the website Graduate Fog, which has campaigned against exploitative work experience, and which discovered that interns were being retrospectively paid, Arcadia said cheques were issued after an “internal review” of intern placements.

Miss Selfridge intern Emily Wong said she spent a month, starting in April 2011, doing what she called “dogsbody work” for the company.

Wong, a 23 year-old graduate of Royal Holloway, University of London, said she and other interns spent their four weeks there photocopying, scanning images, sending clothes to journalists and organising clothes that had been sent back. They also tidied the fashion cupboard, which she described as a walk-in, windowless wardrobe stuffed full of clothes.

She said the company gave her only travel to cover zones 1-6, though she commuted from Worthing, West Sussex, five days a week, and £2.50 a day for lunch.

Wong, who received a cheque for £851 ($1320), added that she found the experience a waste of her time and that interns were excluded from any serious meetings or learning experiences. She also told UK tabloid the Guardian that interns would be left to their “menial” tasks without much supervision and then go on to train other unpaid interns who would arrive at head office.

She said she met 10 other interns in the PR department during her time at Arcadia. ”At the time, I agreed to work at Arcadia for free in the hope that it would lead to a paid job. However, since then I’ve done several more internships – mostly paying expenses only – with other companies and I’m now furious about the whole intern thing,” Wong said.

“I’m glad Arcadia have finally paid me – but they should have done it at the time, not a year later. They should never have allowed me to work for free. As I now know, the minimum wage law says that anybody who does the job of a ‘worker’ must be paid at least the minimum wage for their labour,” she said.

A second intern who has also now been paid, but declined to be named, confirmed the existence of the windowless stock cupboard and described doing the same basic tasks for a different section of Arcadia.

Wong said she complained to HMRC about her lack of pay and it is understood that HMRC has received other complaints about unpaid interns.

Arcadia’s billionaire owner, Sir Philip Green, has said: “We’ve done everything we think we’re supposed to do. We think we’ve been leaders in education in the fashion retail business. We’ve built an academy. We’ve got 700 kids working. We try to encourage other people. We’ve done our job.”But when asked further questions about the payments, he said: “We’re not interested in getting into a running debate about who said what to who and this that and the other”.

In a statement the company said: “Having had a thorough review with regards to interns, the company is perfectly satisfied that it has complied, and is fully compliant, in this area.”

A spokesperson for HMRC said: “HMRC’s position has always been clear regarding the national minimum wage – we want employers to get it right first time.”

“Working with companies is the best way to ensure they pay all their workers what they legally owe. There is no excuse for not paying the minimum wage, and HMRC will relentlessly pursue those who try to bend or break the rules. Anyone who thinks they may not be paid what they are legally entitled to should call the free Pay and Work Rights helpline on 0800 917 2368.”

Tanya de Grunwald, founder of Graduate Fog and author of How to Get a Graduate Job in a Recession said, “This is a massive victory in the battle to end unpaid internships. Pressure is building on big companies, who are finally getting scared about the possible consequences of ‘hiring’ young staff without paying them a wage for their work. Frankly, they should be scared. For too long, too many employers have viewed young people desperate for experience as a source of unlimited free labour. That is completely unacceptable.

“While I’m pleased that Arcadia has made these payments, big questions remain. If they admit these interns were entitled to wages, why weren’t they paid at the time? And will other companies follow suit, making mass pay-outs to those who have worked for them unpaid in the past?”