The list ranks 50 family office businesses by assets under management. In its report, the news service said HSBC’s business oversees $102 billion for families. In second place is Bessemer Trust Co, based in New York, with $44.5 billion of AuM.

Such business units have been set up by firms to tap into an expected continuation of family wealth growth; in Asia, for example, firms such as UBS have developed teams to exploit a fast rise in the number of Asian ultra high net worth individuals.

Some seven of the top 10 providers of family-office services in the Bloomberg Markets rankings are owned by or affiliated with large banks. Besides HSBC, the other firms include UBS (third), San Wells Fargo (5) and SunTrust Banks, which has purchased 70 per cent of Florida-based GenSpring Family Offices (7) in 2001.

The amount of money managed by the 50 top firms has expanded by 17 per cent, to $477 billion, in 2010 from 2009.

Explaining how it chose to list which firms, Bloomberg these family office businesses had to serve more than one family and provide the amount of assets they oversee and the number of clients they serve. Those that declined were excluded.