Two veteran rag trade brothers who came out of retirement to help turn around the fortunes of Marks & Spencer’s clothing business delivered as much as £72m to the bottom line last year.

Neal and Mark Lindsey, 65 and 62, were hardly mentioned when M&S’s chief executive, Marc Bolland, this week triumphantly unveiled the company’s first annual rise in profits in four years.

Recruited last year with the offer of a three-year contract – under which, according to industry gossips, they stand to earn millions of pounds a year – the brothers have been shaking up the way M&S buys and makes its clothing.

The two multimillionaire Londoners are described by fellow fashion industry insiders as charismatic hard men who know the international network of clothing suppliers from top to bottom. Now based in Hong Kong, although they retain homes in the UK, they’re friends with celebrity businessmen such as the Topshop boss Philip Green and Richard Caring, owner of a string of restaurants and private clubs including the Ivy, who also started out supplying clothing to the high street.

Unlike those two, however, who are frequently been photographed and have seen their business lives scrutinised, the Lindseys have stayed out of the limelight.

“They don’t fit the normal executive format. They have been successful because they are gamblers,” says one industry insider. “But they have always lived a colourful lifestyle. Both live life at 100 miles an hour.”

“They were party animals, two chippy guys from London,” says another industry veteran who knew the Lindseys in the 1980s.

The Lindseys are best known for helping M&S’s rival Next become more efficient in the way it buys clothing. Their efforts helped build Next into a far more profitable business than M&S, despite the latter ringing up more than twice the level of sales each year.

Those who know them say the Lindsays learned their trade working Saturdays and school holidays in their uncle’s menswear store in Golders Green in the 1960s.

Both then moved on to work for Rael Brook, a shirtmaker then in its heyday, and in the late 1960s they began importing from Hong Kong and India under the brand Southern Comfort.

In 1975 they started Nashville Fashionwear, a joint venture with Raybeck, a clothing manufacturer and retailer which at one point owned 300 stores including the Lord John and Berkertex chains.

The pair helped Raybeck move into menswear and built up a formidable range of contacts with overseas manufacturers. The business made own-label clothing for high street retailers including the Burton Group, which then owned Debenhams and Topshop, as well as their own Nashville brand.

They spied the potential business opportunity in making clothing where materials and labour were far cheaper than the UK, and in the mid-1970s the pair moved to Hong Kong to mastermind operations from there.

“It was an exciting time in the industry and they were among the big boys, stars among it all,” says one industry source. “They were famous for their fantastic parties.”

Neal is tall and slim while his brother Mark is shorter and broader. “They’re known in the industry as the Mitchell brothers,” says one former colleague, referring to the characters from soap opera EastEnders.

In an 1989 interview with the trade journal Men’s Wear, Neal explained their relationship. “We have always worked together and I think the people that know us, whether they like us or not, will recognise that our relationship is the strength of our business. Because we’re brothers, there’s a lot we don’t have to say to each other because we both know what the other is thinking. And, of course, we both have total trust, which is a big help in a partnership.”

Having built a reputation with Nashville, the pair were approached by Richard Caring to help set up a sourcing operation for Next in “near east” countries including Turkey, Romania and Sri Lanka. Nashville merged into Caring’s ICD Group, and the Lindseys ran and co-owned the business, known as NV Production, with Neal living in Sri Lankaand Mark based in Romania.

In 2002 Caring and the Lindseys, who owned just under half of NV, sold out to Next and the Lindseys stayed on to work directly for the retailer. The business was merged with Next’s far east buying operation to become Next Near East in 2005 and the brothers ran the whole show until they retired in 2005. They were set to put their feet up before being approached by Marks & Spencer.

“They will make millions if they get the sourcing right. I don’t think they would have come out of retirement otherwise. They are already very wealthy guys,” says one friend.

They will be rewarded for every point of extra profit margin they can secure for M&S, and so far it is going well.

M&S’ gross profit on its clothing and homewares business rose by £24m last year as margin gains compensated for a 2.5% fall in sales. There was a 1.9 percentage point rise in gross margins on clothing and homewares, and M&S credited 1.8 percentage points of that gain to cutting better deals with suppliers – a figure analysts said was equivalent to about £72m.

One of the UK’s oldest clothing retailers, M&S has been struggling for years to make changes to the way it buys clothing in order to become more profitable. While Bolland has tried to emphasise that a team effort is behind the recent changes, industry experts insist the recent improvement is largely down to the Lindsey brothers.

“They know what they are doing and have enormous range of contacts. M&S has never got hold of its supply chain. They have too much history with big UK organisations with big UK overheads. M&S needed someone without that history or emotional attachment,” says one industry source who knows the Lindseys well.

Some long-term M&S partners, including Dewhirst and Courtaulds, are among a string of suppliers who have lost business or seen their profit margins squeezed as the Lindseys renegotiate terms. Israeli suit manufacturer Bagir Group was forced to issue a profits warning after M&S cut orders in May last year. The Lindseys have torn up relationships that have lasted decades and helped implement a new way of working in which more clothing is designed in-house.

Until recently, M&S had only a handful of its own designers, instead using “full service” suppliers who would present a range of different fashions for M&S buyers to choose from. Now there are 130 in-house design staff and another 30 freelancers. That is giving the retailer more control over the fashions it sells and more freedom to find the best deals with suppliers.

In 2013 M&S bought a fifth of its clothing directly from suppliers; now it is about 35%, and the company intends to increase that proportion to 60% by 2017.

Industry sources report that the Lindseys have introduced an auction system for some basic clothing lines, asking a number of different suppliers to offer their best price on each item. Some rivals suggest that the change of approach, moving away from long-established supplier relationships, carries the risk that M&S will lose the high ethical and sustainability standards that it has built its reputation on.

But an insider said M&S would not take big risks with that reputation, even if it did offer bigger profits. “Regardless of the agenda on margin, someone is going to make sure they don’t give [on ethical standards]. M&S’s reputation is massive, I’m not sure they would take that risk.”