Shares in Capita, the firm that operates London's congestion charge, today raced to a four-year high after it delivered a big rise in half-year profits.

Capita reported pre-tax profits of £92.4m in the six months to 30 June, up from £74.5m a year earlier. Sales increased to £845m.

Apart from a jump in profits, investors were encouraged by Capita's bullish outlook.

"Our businesses are in superb shape to deliver incremental growth," said Rod Aldridge, the non-executive chairman.

Mr Aldridge stepped down as chairman in March after allegations - dismissed by Capita as "spurious" - that his £1m loan to Labour led to government contracts.

Capita said it had won a significant volume of new business, strengthening its position as the market leader in providing outsourcing services to the public and private sectors.

This year, Capita announced £655m of major contract wins and renewals, including a £132m contract with the BBC and a contract worth £120m with the Department of Trade and Industry.

"Capita has made considerable progress in the first 6 months of the year, reflected in another period of excellent financial results," Capita said.

In lunchtime trading, Capita shares were up 11% at 518p.