The Northern Rock debacle produced its first senior casualty today as Matt Ridley, chairman of the run-hit bank, announced plans to quit. The Rock named Bryan Sanderson, former chairman of Standard Chartered and BUPA, as his successor.

It was not immediately clear if Mr Ridley would receive a payoff.

The Rock announced today that Mr Ridley and the rest of the board now believed the time was now right for him to go. He had until now been asked to stay while new funding arrangements were put in place and in order to appear before the Treasury Select Committee.

As chairman and a long-standing director who approved Northern Rock's business strategy for many years, Mr Ridley has been accused of developing and fostering the unusual business strategy which led to the catastrophic loss of confidence in the bank. However, he has argued that the board was not to blame and that the run was entirely a result of the unforeseeable credit crunch.

His lack of banking experience - he is a full-time author and zoologist - has also come under scrutiny. As chairman he was paid £300,000 a year. It is understood he will receive no pay-off.

Mr Sanderson, who unexpectedly resigned from Standard Chartered last November, will take over as soon as his appointment has been approved by the Financial Services Authority.

Sir Ian Gibson, the senior independent director at Northern Rock, said: "I want to thank Matt Ridley for his hard work as chairman since 2004 and particularly for his commitment during the very difficult circumstances of the last few months."

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