Royal Bank of Scotland has suffered a damaging but not yet destructive exodus of top staff and some areas of investment banking had lost significant numbers, the British bank's chief executive said.

RBS's investment bank posted a four-fold jump in profits on Friday but said earnings from the unit and across the industry would fall from those lofty half-year levels.

Stephen Hester said the percentage of top performing staff to leave the bank had doubled in the first half from a year ago, but that was from a modest level.

It's damaging but not yet destructive, he said at a news conference. We need to make sure it doesn't get destructive and hopefully stops being damaging.

There are some specific pockets within the investment bank where because of the return to profits around the world (there has been) a particular intensity of hiring, and we have lost significant numbers of people in those areas, Hester said.

Global Banking and Markets (GBM), RBS's investment bank arm, has been hit by poaching from rival firms and has also exited from some areas. Its headcount fell by 1,500 staff, or 8 percent, in the first half.

Hester said the bank needed to pay competitively to retain and hire top talent and was offering some guaranteed bonuses, but pay deals were limited and structured with the potential for clawback and deferral.

GBM's operating profit was 4.9 billion pounds ($8.2 billion) in the first half from 1.1 billion a year ago, providing a rare bright spot as the part-nationalised bank reported a 1 billion pound loss.

GBM's income more than doubled from a year ago to 7.8 billion pounds, including revenue of 4.8 billion in the first quarter alone.

The performance in Q1 and in the second quarter are much higher than trend lines. Predicting investment banking revenues quarter by quarter is a fool's game, but we are clearly saying that normal revenues in the business are significantly lower than the revenues that we and other investment banks reported in the first bit of this year, Hester said.

BUMPER CROP

GBM's quarterly revenues averaged near 2 billion pounds during 2008.

RBS joined rivals including Barclays, Credit Suisse, JP Morgan and Goldman Sachs in reporting bumper investment bank profits.

Lower interest rates, hefty government bond issuance, lively currency markets, volatile markets and wide bid/offer spreads all swelled revenue.

Hester is dramatically reshaping GBM to make it far less risky and expects the business to produce about a third of future group earnings and a return on equity of 15 percent by 2011 and 15-20 percent by 2013.

Its credit markets income hit 1.5 billion pounds from a loss a year ago, its rates money markets income more than doubled to 1.4 billion pounds and rates flow income rose 38 percent to 1.9 billion. Currencies and commodities income rose by 40 percent and 34 percent respectively.

GBM, built up aggressively under former CEO Fred Goodwin, reported an operating loss of 11 billion pounds in 2008 after suffering trading asset writedowns of 5.8 billion pounds and credit market writedowns of 7.3 billion pounds. ($1=.5966 Pound) For a column by Margaret Doyle on RBS. (Additional reporting by Clara Ferreira-Marques; editing by Karen Foster)

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