The India-born brothers topped the 'Asian Rich List 2015' released here and the annual rankings showed that they had added 2 billion pounds to their personal fortune in a year to be worth an estimated 15.5 billion pounds.
The Hinduja brothers, who head the Hinduja Group global conglomerate spread across defence, banking, automotive and power sectors, are also the richest men in the UK.
"We are expanding in a big way," G P Hinduja had recently said while talking about plans to take up the Narendra Modi-led government's 'Make in India initiative' to expand the group's manufacturing base in India.
This year's analysis showed that the UK's richest Asians have added an estimated 3 billion pounds to their fortunes to be collectively worth 54.5 billion pounds.
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It also showed that low interest rates and slowing economic growth have hit the UK's wealthiest as the pace of their wealth creation slowed by more than half last year to just 5 per cent.
While 59 of the 101 millionaires have seen an overall increase in net worth, 30 have remained static and 12 have seen a drop in valuation.
Mittal is ranked second in this year's tally.
Last year's highest new entry to the list, plastics tycoon Prakash Lohia, is now the UK's third richest Asian with an increase in net wealth of 1 billion pounds, taking his fortune to 3 billion pounds.
Discount retailer B&M Group founders Simon, Bobby and Robin Arora come in at fourth with 2.1 billion pounds, with London Stock Exchange listed Vedanta Group chief Anil Agarwal completing this year's top 5 with an estimated wealth of 1.5 billion pounds.
"The list shows the remarkable resilience and diversity of Asian businesses in the UK," he said.