Dell plans to consolidate its worldwide marketing, advertising and communications operations into a single new public relations unit led by WPP, the UK advertising group.

The advertising pact, worth $4.5bn in billings over the next three years, will come as a significant fillip for WPP as Sir Martin Sorrell, its chief executive, has been trying to persuade investors that they are undervaluing the company’s share price. WPP’s stock price has fallen 18 per cent in the past six months, underperforming the London market.