LONDON (Bloomberg) — Old Mutual Plc rose the most in a month after Cevian Capital AB, a Swedish investment firm with more than 3.5 billion euros ($5 billion) under management, said it had acquired a 4.1 percent stake in the company.

Old Mutual, which closed its Bermuda-based US life insurance unit to new customers in March, rose 5.1 pence, or seven percent, to 78.4 pence in London trading, the biggest gain since April 30. The stock has advanced 43 percent this year, making it the best performer in the 33-member Bloomberg Europe 500 Insurance Index.

"We believe that the market has failed to recognise the value of the company's stable core businesses, which have performed well, even in this extreme macro environment," Martin Oliw, a partner at Stockholm-based Cevian Capital, said yesterday in a statement.

Cevian, which holds stakes in companies including Swedish truckmaker Volvo AB and Munich Re, the world's biggest reinsurer, supports the strategy set out by Old Mutual chief executive officer Julian Roberts, Oliw said in the statement.

In an interview last month in London, Roberts said growth would be boosted by Old Mutual's long-term savings unit in the UK, known as Skandia. Revenue from businesses in South Africa and the UK increased last year, even as net income fell 55 percent to £441 million after hedging failures at its US unit and declines in the value of investments.