One of Royal Bank of Scotland’s top dept bankers is believed to have quit amid the continued turmoil in the credit markets.

Rick Caplan, managing director and co-head of the US collateralised debt obligation (CDO) unit, has left as the bank “resizes” RBS Greenwich Capital Markets, the US securities division of RBS.

His departure was first reported on the website of the securities industry newspaper, Financial News.

Mr Caplan's move leaves Fred Matera in sole charge of the RBS CDO unit.

RBS was not immediately available to comment.

In a statement, Mr Matera said: “We have resized our CDO business to meet market demand. We intend to continue to be an active player in the CDO market going forward.”

Mr Caplan is the second senior debt banker to have quit in less than two weeks. Ed Cahill, the former head of Barclays Capital’s CDO business and the executive responsible for creating SIV-lites, left the bank last week.

CDOs are packages of mortgages parcelled up and sold on to investors. The collapse in the US sub-prime mortgage market has led to a crisis in the CDO market, with investors left unable to price their assets.

Meanwhile, the German finance ministry has called for greater co-operation between the supervisory authorities of German banks, following the near collapse of IKB Deutsche Industriebank AG and SachsenLB earlier this month.

The Wall Street Journal quoted a spokeswoman from the finance ministry as saying that the crisis at the two banks had "renewed debate within the ministry over how best to regulate banks in Germany". She added that, initially, the ministry wanted to "intensify co-operation between different supervisory authorities," before a general overhaul of the system of banking supervision.

In Germany, banking supervision is divided between the markets regulator, BaFin, and the Bundesbank, Germany's central bank. A spokesman for the Bundesbank declined to comment to the Journal.

As part of the division of supervisory responsibilities, according to BaFin, the Bundesbank is responsible for signing off on annual reports of banks. BaFin is responsible for conducting special audits of banks. The Journal says that, in dealing with regulators, German banks have complained to the finance ministry that the dual regulatory system can be confusing and should be simplified.

Both IKB and Sachsen were nearly toppled when the global liquidity crunch made it impossible for key affiliates to sell commercial paper and repay creditors. As a result, IKB needed a sizeable bailout and Sachsen was sold to another German state-owned bank, Landesbank Baden-Württemberg.

As global markets felt the impact of the credit crunch in July – triggered by anxieties about the troubled US sub-prime mortgage industry – Germany's Finance Minister, Peer Steinbrück, postponed a meeting on August 8, at which he was expected to present the finance ministry's proposal for an overhaul of banking supervision.

According to the Journal, the plans, which are being reworked, will not be presented before the end of the year. BaFin and the finance ministry will await the outcome of special audits on IKB and Sachsen before moving forward with changes.

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