One of Volkswagen's largest investors, US fund manager Tweedy Browne, has sharply criticised the change of leadership at Volkswagen and in particular, supervisory board chairman, Ferdinand Piech.

A partner in the investment house, Tom Shrager, told Handelsblatt newspaper that the fact that a CEO, who is so obviously successful, can be removed from his position so easily, raises serious questions about corporate governance at Volkswagen and the role of Piech.

Tweedy Browne is the fifth largest investor in Volkswagen and, with 2m shares, currently holds a stake worth around 1%.

Tweedy Browne has been concerned about Porsche's influence on Volkswagen in the past, but with just a 1% shareholding, it has failed to exert its own influence on the board.

Much more influential is Volkswagen's second largest shareholder, the state of Lower Saxony (Niedersachsen). Its board representative, president of Lower Saxony, Christian Wulff, has also been critical of Piech and a possible conflict of interest as head of both Porsche and Volkswagen.

Wulff has set out a number of challenges for Pischetsrieder's designated successor, Martin Winterkorn, in the German newspaper, Bild am Sonntag.

Wulff detailed four clear requirements for Winterkorn. Firstly he should continue the consolidation and restructuring programme that Pischetsrieder set in motion, improving efficiency and quality, and developing better cooperation between various parts of the company such as engineering, purchasing and production to avoid duplication of effort.

Secondly Winterkorn should improve returns and guarantee jobs.

Thirdly, Winterkorn should become north German 'in heart and mind', as all the six German plants are in north Germany.

Finally Winterkorn should be bring the same success to the whole company as he brought to Audi, as this is not just in the company's interest, but also in the interest of the country and of Lower Saxony - the state holds a 20.8% stake in Volkswagen.