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Describing a more "challenging operating environment", Vodafone chief executive Arun Sarin announced that revenue in the financial year ending 31 March 2009 "would be around the bottom" of the predicted £39.8 billion to £40.7 billion range.

Sarin claimed that alongside signs of economic slowdown, profits had also been hit by a competitive voice market in the UK.

The news caused share prices to drop around 11%, though the company says cost cutting measures will allow it to meet its profit forecast for the current financial year.

Despite the slowdown, Vodafone says it still expects to make an operating profit of around £11 billion to £11.5 billion, buoyed by strong growth in emerging markets.

The company also announced that it had added 8.5 million subscribers in the financial quarter ending June, taking the total to 269 million and boosting revenues to £9.8 billion, a 19.1% increase on the year earlier.