Stephen Whittaker has left his job as joint chief investment officer at New Star Asset Management with immediate effect.

John Duffield, New Starâ??s chairman, asked Mr Whittaker to leave on Friday after what Mr Duffield called "a long period of underperformance".

Mr Whittaker was in charge of the £343m UK Growth Fund, which has fallen 52.4 per cent over the past two years compared with an average 31.2 per cent fall among peer funds.

The fund attempts to achieve long-term capital growth from UK stock investments.

Trevor Green, who already manages the equity portion of the Managed Distribution Fund, will take over the UK Growth Fund immediately. New Star is already in discussion with potential candidates for the role of chief investment officer.

Mr Duffield said in a statement: "We are moving swiftly to restructure our fund management activities in response to the bear market."

The company is also merging some of its smaller and poorer-performing funds as it looks to improve on some poor results, which have led to its share price nearly halving in the past year. The shares were down a further 5 per cent at 23p in afternoon London trading.