UBS has completed an overhaul of its corporate governance structure and has issued new organisation regulations which are effective immediately.

The changes, stemming from an announcement at the bank’s last AGM in April, come as UBS, the world’s largest wealth manager, faces huge challenges in the US, the UK and in its Swiss homeland. They follow sustained criticism from major shareholders and industry analysts.

The main changes are a clear separation of the roles and responsibilities between the board of directors and executive management, along with a strengthening of the oversight role of the board through the operation of its committees, the Swiss bank said in a statement issued today.

Four members of the board have decided to resign their positions and as a result, an extraordinary general meeting will be held on 2 October 2008 to elect four new members. The resigning members are Stephan Haeringer, Rolf Meyer, Peter Spuhler and Lawrence Weinbach.

Sergio Marchionne has been appointed senior independent director and continues as the company’s non-executive vice chairman.

UBS says that the new model clarifies the separation of responsibilities between the board and the executive management. The board will have a clear strategy setting responsibility, and it will supervise and monitor the business. The chief executive and the group executive board will be fully responsible for the executive management of the bank. The duties and responsibilities of the former chairman’s office are now allocated to a greater number of committees of the board, including new risk and strategy committees. The remits of the governance and nominating committee and the human resources and compensation committee have been expanded.

Olivant, the investment firm led by former UBS president Luqman Arnold, said it welcomed the changes.