Srichand Hinduja, Gopichand Hinduja
Srichand Hinduja talks on a mobile telephone, accompanied by his brother GopichandReuters

The cover of today's Sunday Times magazine features a photograph of a smiling man in a tasteful suit sitting on an expensive-looking chair. No wonder he looks pleased with himself: Gopi Hinduja and his three brothers, known in their native India as the Fab Four, are collectively worth £11.9bn, making Srichand, 78, and Gopi, 74, who live in London, Britain's wealthiest men.

But who are the Hinduja brothers, and where and how did they make their mind-boggling fortune? In its profile, the Sunday Times claims the Hindujas - all four of whom are teetotal, vegetarian and religious - built their empire "from nothing", from "humble beginnings" in the Indian subcontinent, and are now neighbours to the Queen of England - a classic rags-to-riches story.

Labour MP Peter Mandelson had to resign over the Hinduja affairLeveson Inquiry

Except it's not quite that simple. For one thing, the family business was started by father Parmanand, in 1914 when he arrived in Mumbai (then Bombay) to learn the art of commerce and founded the Hinduja Company. By 1919 Parmanand had expanded operations abroad, moving operations to Iran where the company remained until the overthrow of the Shah in 1979.

Sri and Gopi moved to London, where they now own a six-storey home in Carlton House Terrace. The third brother, Prakash, lives in Geneva and the fourth, Ashok, remains in Mumbai. Sri – also known as SP – took over control of the global company following the death of his father in 1971.

Over the years, the Hindujas - like many global businesspeople - have found themselves mired in a number of controversies. Having donated £1m to the "Faith Zone" of the Millennium Dome, it transpired that then Northern Ireland Secretary Peter Mandelson had speeded up Sri's application for a British passport, and had to resign for a second time in his career.

The brothers were also accused of accepting "kickbacks" from Sweden's now-defunct Bofors Company as part of a deal to buy guns. The brothers always denied the charges and the case was eventually thrown out by the Delhi High Court.

When the family's Ashok Leyland company, based in India, announced it was to sell 100 army vehicles to the Sudan army, comedian and campaigner Mark Thomas claimed the deal contravened UK arms export legislation. Thomas filmed a report in 2005 which the BBC's Newsnight pulled after being threatened with legal action. The Hindujas claimed the trucks weren't for military use and family lawyer Shahrokh Mireskandari told The Guardian the Sudan contract "was always meant to be a humanitarian contract".

In 2012, Mireskandari was banned from practising as a solicitor after a newspaper investigation revealed many of his legal qualifications were bogus.

Despite these controversies, the Hinduja brothers remain some of the most powerful people in world business, their friends including former US President Bill Clinton and numerous UK politicians. The brothers have also used their status for a range of good causes including the funding of scholarships, hospitals and charitable foundations.

The brothers may be worth more than most small countries, but are they happy? Judging by Gopi's grin on the front cover of today's Sunday Times, they certainly are...