Amid concerns growing among ministers that the Government's advertising has been thrown into turmoil, Alistair Darling, Stephen Byers' successor as the transport secretary, has approved the go-it-alone plan, but for a limited period only, after which it will be reviewed.
The move raises the prospect that the DoT could be brought back into COI's fold if running its own campaigns and rosters does not prove cheaper than paying 1.75 per cent commission to COI.
The cabinet office minister in charge of COI, Douglas Alexander, is said to be "concerned the DoT breakaway may undermine COI's long-term future.
He is worried that the DoT move has contributed to the resignations of Carol Fisher as the COI chief executive and Derek Dear as the chairman of the Advisory Committee on Advertising, which monitors COI.
Alexander, who was handed responsibility for COI this week, will hold urgent talks with Dear in an attempt to head off the possible threat of more resignations by other ACA members, who are drawn from advertisers.
One ministerial source said: "Douglas Alexander is anxious about the situation. But he cannot over-rule Alistair Darling, who is in charge of the DoT's advertising. The compromise is that the DoT plan will go ahead but will be reviewed after 12 months."
COI officials hoped that the reshuffle that followed the resignation of Byers might halt the shake-up. The Department of Transport, Local Government and the Regions was scaled down to take charge solely of transport, and its advertising budget was cut from £18 million to £12 million as a result.
However, Darling concluded that despite this it was too late to stop the trial.