But since interest rates tanked in the wake of the global financial crisis, they have been hiring in-house advisers, often ex-investment bankers keen to do business with former colleagues.

They are helping family offices to look for more creative ways of earning a return than simply handing their cash over to fund managers, whose 2 percent annual fees and 20 percent on any profit earned are falling, but not fast enough for some.

Robert Bibow, Managing Partner at private investment advisor Bidwell Capital and a former employee of Goldman Sachs and Deutsche Bank, cites one client, a member of the Saudi royal family, who decided that after 20 years of investing in private equity funds to focus only on investing directly into deals.

Trust

Wealthy families made a string of high-profile deals in 2014. The Qatari royal family poured 1.75 billion euros ($2 billion) into Deutsche Bank's 2014 rights issue, while the billionaire March clan's holding firm Corporacion Financiera Alba took an 8 percent in Spanish airport operator Aena ahead of its initial public offering (IPO) this year.

Having a family buy into a new share deal can be a trump card for investment bankers because they are willing to tie up their funds for a long time.

"More and more in the context of pitching equity capital market (ECM) mandates, having access to such anchor investors is a differentiating factor," said Sam Losada, head of International Strategic Equity Solutions and co-head of Global Rates & Currencies Origination at BoA Merrill Lynch.

Family offices offer investment banks the possibility of a lengthy and lucrative relationship and are also often easier to deal with than institutional investors whose decisions are often delayed by internal committees.

"If they call us with a deal opportunity and we respond in 24, 48 hours, they like that," said Marc Meyohas, whose private equity vehicle Greybull Capital invests money from his own "entrepreneurial industrialist" family, and one other.

UBS said it expects to earn around 260 million Swiss francs ($297 million) in Global Family Office revenues outside the United States in 2014. Within that, earnings from direct deals grew fastest of all, although it is still dwarfed by income from the foreign exchange division for example.