Standard Life and Hermes are set to join Morley Fund Management in a protest against Arun Sarin, Vodafone's chief executive, at the mobile phone company's annual meeting tomorrow.

Vodafone is braced for institutional investors holding about 10 per cent of its shares to vote against Mr Sarin's re-election at the meeting, according to close observers of the company.

Investors holding a further 5 per cent of Vodafone's shares could abstain, the observers said.

Roughly 440,000 investors in the Republic own shares in Vodafone, with most of the holdings a legacy from the company's purchase of Eircell from Eircom in 2001.

The protest against Mr Sarin is not expected to force his immediate departure, but it will intensify pressure on Sir John Bond, Vodafone's incoming chairman, to decide quickly whether to find a new chief executive.

Mr Sarin, meanwhile, will be under pressure to show rapid progress on Vodafone's new strategy to deal with slowing revenue growth by cutting costs and getting customers to make greater use of mobiles in their homes.

Standard Life Investments, one of Vodafone's top 10 investors, is expected to vote against Mr Sarin's re-election or abstain at tomorrow's annual meeting in London. It declined to comment.

Sources familiar with the thinking of Hermes Pension Management, another big investor, said it would vote against Mr Sarin's re-election.

Vodafone said: "We respect the views of individual shareholders.

"As far as we are aware, the vast majority of votes cast support the board."

Mr Sarin has come under fire from some of Vodafone's big investors since the company warned last November of slowing revenue growth and lower profit margins.

In May, Vodafone reported a record pretax loss of £14.9 billion (€21.8 billon) for its 2006 fiscal year.

Analysts said they expected Vodafone's performance figures for the first quarter of its 2007 fiscal year, published today, to show year-on-year declines in average revenue per customer in core European markets such as Germany, Italy and the UK.