Germany's public prosecutor has launched an investigation into Vodafone's newly-knighted chief executive Sir Chris Gent for alleged irregularities during the mobile phone giant's takeover of Mannesmann.

The Duesseldorf-based prosecutor said on Monday that the probe also targeted former Mannesmann chief executive Klaus Esser, IG Metall trade union head Klaus Zwickel and the chairman-designate of Deutsche Bank, Josef Ackermann.

In total, according to German media reports, 10 people are now included in the investigation, which has been in preparation since June.

Vodafone's takeover of Mannesmann - one of the bitterest battles in German corporate history - was concluded last year.

Vodafone and Deutsche Bank have both declined to comment on the latest reports, while IG Metall has denied the allegations.

Under investigation

The investigation follows a Mannesmann executive committee decision to award a 60m Deutschmark (�19m; $28m) golden handshake to Mr Esser, who now works for a US finance company.

Other Mannesmann executives also received money, making total payouts of 120m Deutschmarks.

Investigators are examining the pay-offs to the former executives to determine whether they were too high or not commensurate with the executives' duties or the financial state of the company, as required by German share law.

According to German magazine Der Spiegel, there are suspicions that the payments were in effect bribes, aimed at compensating Mannesmann executives for dropping their resistance to Vodafone's hostile bid for the firm.