Orbis, which owns around a fifth of Cable & Wireless Worldwide (CWW) stock, said it would not try to block a takeover bid for the firm by Vodafone.
Despite initially saying the offer of 38p a share was too low, Orbis said it now believed the deal was inevitable.
It said that it believed Vodafone's bid would ultimately prove successful and there was no point in prolonging the takeover process.
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Getting Orbis on side was critical for CWW as it needed 75% of shareholders to vote for the deal at a meeting on Monday for it to go through.
Reports said it had secured 59% prior to Orbis' acceptance of the deal.
In April CWW's board unanimously recommended shareholders take the offer on the table.
At the time Vodafone said the offer was a premium of 92% to the closing price of 19.8p per CWW Share on February 10th, 2012 - the last business day before the offer period.
The share price has now risen to match the bid, sitting at 37.8p on Monday morning.
"Based on the information announced by CWW today which was shared with us on Saturday and following discussions with CWW, we now believe that the CWW Scheme of Arrangement will eventually succeed, even if Orbis were to vote against it today," Orbis said.
"In these circumstances, our opposition would only serve to prolong the process because the company would likely adjourn today's meetings to secure the necessary votes; this is not in the interests of any CWW stakeholder."
Faced with this reality, Orbis said it intended to vote in favour of the scheme today.
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