Val MacQueen writes

Those expelled from East Africa were third generation immigrants to Africa, and had created assets and wealth. Which is why Idi Amin was so interested in them. Now, those families are again third generation immigrants, this time to Britain, and again they are rolling in wealth. How was this extraordinary feat accomplished twice?

The World Bank’s book Where is the Wealth of Nations? does not list Uganda, but it gives the per capita wealth of Kenya as $6609. The CIA world factbook gives per capita GDP of Uganda as $1700, compared with $1200 in Kenya. If wealth and GDP are proportional, that means that per capita wealth in Uganda is less than $10,000. If you multiply that by the 40,000 South Asians made refugees by Idi Amin, they would now be worth $400 million collectively if they had remained in Uganda and had the average economic status of Ugandans (although presumably they would have been well above average). MacQueen’s story lists several individual former refugees who are worth more than $400 million.