Britain's two largest advertisers, with an annual combined buying power of more than £270m, have called on the Competition Commission to block the merger of Carlton and Granada.
Consumer goods giant Procter & Gamble and the Government's advertising agency, COI Communications, say a combined ITV sales force would be anti-competitive. Neither group wants the £2.4bn merger to go ahead in its current form.
"We don't see how this merger can proceed," said Bernard Balderston, P&G's associate director of UK media.
P&G is lobbying through the Incorporated Society of British Advertisers, which is due to meet the Commission on Tuesday.
COI, which has written to the Commission with its concerns, believes that allowing Carlton and Granada to combine its sales forces would set a dangerous precedent. A spokeswoman said: "It could result in the current seven major sales organisations being reduced to only three selling around 150 channels."
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