A shadowy investment group is agitating for Vodafone, the world’s largest mobile operator, to consider a sale of its American operations and a review of its debt structure.

Efficient Capital Structures has written to Vodafone demanding that it submit at its annual meeting next month resolutions concerning a potential restructuring.

The group — whose members are understood to include John Mayo, the former Marconi executive — wants Vodafone to re-assess its debt levels and to pledge to provide more “visibility” on the value of Verizon Wireless, its joint venture in the United States.

Vodafone, which was caught unawares by the request yesterday, confirmed receipt of a letter. In a statement it said: “Vodafone has received this evening a letter from Efficient Capital Structures claiming to require Vodafone to submit a number of resolutions to the company’s annual general meeting on July 24, 2007, concerning potential restructuring options for the company.

“Vodafone will review the contents of this letter and will be making a further announcement in due course.”

It is understood that the group will issue a more detailed response today after it has confirmed whether it is obliged to entertain the request.

Under company law, such requests must be treated seriously by the targeted business if the pressure group holds 5 per cent of its shares or if the request comes from 100 shareholders.

The move on Vodafone is the latest example of shareholder activism that has beset the group, as well as other companies, of late. The Children’s Investment Fund, another activist investment group, has been prominent in the battle to take over ABN Amro.

The pressure from Efficient Capital Structures also comes just as Vodafone looked to have put behind it one of the most turbulent periods of its history.

Last year a flagging share price and perceived lack of strategy by Arun Sarin, its chief executive, triggered a shareholder revoltm, which culminated in shareholders with 15 per cent of the stock refusing to back the chief executive at the group’s annual meeting.

Although Mr Sarin successfully saw off that discontent, the mobile group recently has found itself at the centre of heightened speculation about its future. Vodafone’s share price has jumped 12 per cent in the past two weeks in huge trading volumes. Speculation had centred on a possible bid from an American buyer, such as AT&T, or an approach from private equity consortium.

Rumours swirling around the group were fuelled further by a declaration from Mr Sarin himself at the group’s annual results last week that, despite its size, with an enterprise value of $200 billion, Vodafone was not too big to be taken over.

The group is consistently quizzed on its intentions on its American venture with Verizon Wireless. In addition, a growing body of analysts and other stakeholders have questioned why the company does not seek to gear up and enhance the level of its return to shareholders.

Times Recommends

• Lies and cover-up at MG Rover exposed by report
• High oil prices push manufacturing costs up
• Primark founder steps down as chief executive